DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
______________________________________________ Maxim Integrated Products 1
For pricing delivery, and ordering information please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
General Description
The DS1857 dual temperature-controlled nonvolatile
(NV) variable resistors with external temperature input
and monitors consists of two 50kΩ 256-position linear
variable resistors, two analog monitor inputs (MON1,
MON2), and an external temperature sensor input. The
device provides an ideal method for setting and temperature-compensating bias voltages and currents in
control applications using minimal circuitry. The variable resistor settings are stored in EEPROM memory
and can be accessed over the 2-wire serial bus.
Applications
Optical Transceivers
Optical Transponders
Instrumentation and Industrial Controls
RF Power Amps
Diagnostic Monitoring
Features
♦ Four Total Monitored Channels (Temperature,
VCC, MON1, MON2)
♦ Two External Analog Inputs (MON1, MON2)
♦ Interface to External Temperature Sensor (LM50)
♦ Two 50kΩ, Linear, 256-Position, Nonvolatile
Temperature-Controlled Variable Resistors
♦ Resistor Settings Changeable Every 2°C
♦ Access to Monitoring and ID Information
Configurable with Separate Device Addresses
♦ Resistor Disable (Open-Circuit) Function
♦ 2-Wire Serial Interface
♦ Three Address Lines for Multiple Devices
♦ Operates from a 3.3V or 5V Supply
♦ SFF-8472 Compatible
Ordering Information
Rev 0; 1/03
PART
PIN-PACKAGE
DS1857E-050
16 TSSOP
DS1857E-050/T&R
16 TSSOP
(Tape-and-Reel)
DS1857B-050
16 Ball CSBGA
A
TOP VIEW
B
C
D
1
16-BALL CSBGA (4mm x 4mm)
1.0mm PITCH
16 TSSOP
324
EXTTMP
A0WPENRHIZ
MON2MON1L0GND
H1V
CC
SCLA1
L1H0SDAA2
DS1857
SDA
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
SCL
A0
A1
A2
WPEN
RHIZ
GND
V
CC
H1
L1
H0
L0
EXTTMP
MON2
MON1
Pin Configurations
DS1857
SDA
1
2
3
4
5
6
7
8
16
0.1µF
15
14
13
12
11
10
9
SCL
A0**
A1**
A2**
WPEN
RHIZ
GND
V
CC
H1
L1
H0
L0
EXTTMP
MON2
MON1
Tx DISABLE
TO EXTERNAL TEMPERATURE
SENSOR, SUCH AS LM50
DIAGNOSTIC
INPUTS
0 TO 2.5V FS
TO LASER BIAS
CONTROL
TO LASER MODULATION
CONTROL
DECOUPLING
CAP
Rx POWER*
Tx BIAS*
*Rx POWER AND Tx BIAS CAN BE ARBITRARILY
ASSIGNED TO THE MON INPUTS.
**ADDRESS INPUTS DETERMINE THE MAIN DEVICE 2-WIRE
SLAVE ADDRESS WHEN ADFIX = 0. THIS ADDRESS MUST BE
DIFFERENT THAN THE AUX DEVICE ADDRESS WHEN ADEN = 0.
V
CC
V
CC
VCC = 3.3V
4.7kΩ4.7kΩ
2-WIRE
INTERFACE
GROUND TO
DISABLE WRITE
PROTECT
Typical Operating Circuit
TEMP RANGE
-40°C to +95°C
-40°C to +95°C
-40°C to +95°C
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
2 _____________________________________________________________________
PARAMETER
SYMBOL
CONDITIONS MIN
TYP
MAX
UNITS
Supply Voltage V
CC
(Note 1) +3.0 5.5 V
Input Logic 1 (SDA, SCL, A2, A1, A0,
WPEN, RHIZ)
V
IH
(Note 2)
V
Input Logic 0 (SDA, SCL, A2, A1, A0,
WPEN, RHIZ)
V
IL
(Note 2) -0.3
V
Resistor Inputs (L0, L1, H0, H1) -0.3
V
Resistor Current I
RES
-3 +3 mA
ABSOLUTE MAXIMUM RATINGS
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage on VCCRelative to Ground.......................-0.5V to +6.0V
Voltage on Inputs Relative
to Ground* ................................................-0.5V to V
CC
+ 0.5V
Voltage on Resistor Inputs Relative
to Ground* ................................................-0.5V to V
CC
+ 0.5V
Current into Resistors............................................................5mA
Operating Temperature Range ...........................-40°C to +95°C
Programming Temperature Range .........................0°C to +70°C
Storage Temperature Range .............................-55°C to +125°C
Soldering Temperature .......................................See IPC/JEDEC
J-STD-020A Specification
RECOMMENDED DC OPERATING CONDITIONS
(TA= -40°C to +95°C, unless otherwise noted.)
PARAMETER
CONDITIONS
UNITS
Supply Current I
CC
(Note 3) 1 2 mA
Input Leakage I
IL
-1 +1 µA
Input Current each I/O Pin 0.4 x V
CC
< V
I/O
< 0.9 x V
CC
µA
V
OL1
3mA sink current 0 0.4
Low-Level Output Voltage (SDA)
V
OL2
6mA sink current 0 0.6
V
Full-Scale Input (MON1, MON2) (Note 4)
V
Full-Scale VCC Monitor (Note 5)
V
I/O Capacitance C
I/O
10 pF
WPEN Pullup Resistor R
WPEN
40 65 100 kΩ
RHIZ Pullup Resistor R
RHIZ
40 65 100 kΩ
Digital Power-On Reset POD
2.2 V
Analog Power-On Reset POA
2.6 V
DC ELECTRICAL CHARACTERISTICS
(VCC= 3.0V to 5.5V, TA= -40°C to +95°C, unless otherwise noted.)
*Not to exceed 6.0V.
0.7 x Vcc VCC + 0.3
0.3 x V
VCC + 0.3
CC
SYMBOL
MIN TYP MAX
-10 +10
2.4875 2.5000 2.5125
6.5208 6.5536 6.5864
1.0
2.0
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
_____________________________________________________________________ 3
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
EXTTMP Input Voltage
V
Conversion Resolution
625 µV
Conversion Accuracy
(Note 9)
mV
EXTERNAL TEMPERATURE
(VCC= 3.0V to 5.5V, TA= -40°C to +95°C, unless otherwise noted.)
PARAMETER
CONDITIONS
UNITS
Input Resolution
µV
Supply Resolution ∆V
CC
1.6 mV
Input/Supply Accuracy A
CC
% FS
(full scale)
Update Rate for MON1, MON2,
Temp, or V
CC
t
frame
20 30 ms
ANALOG VOLTAGE MONITORING
(VCC= 3.0V to 5.5V, TA= -40°C to +95°C, unless otherwise noted.)
PARAMETER
CONDITIONS
UNITS
Position 00h Resistance TA = +25°C
1.0
kΩ
Position FFh Resistance TA = +25°C 40 50 60 kΩ
Absolute Linearity (Note 6) -2 +2 LSB
Relative Linearity (Note 7) -1 +1 LSB
Temperature Coefficient (Note 8) 50
ppm/°C
High-Z Resistor Current I
RHIZ
R
HIZ
= V
CC
0.1 µA
ANALOG RESISTOR CHARACTERISTICS
(VCC= 3.0V to 5.5V, TA= -40°C to +95°C, unless otherwise noted.)
SYMBOL
SYMBOL
∆VMON 610
MIN TYP MAX
0.70
MIN TYP MAX
0.25 0.5
1.25
V
EXTTMP
∆V
EXTTMP
V
EXTTMP
1.779
12.8
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
4 _____________________________________________________________________
PARAMETER
CONDITIONS
UNITS
Fast mode (Note 10) 0 400
SCL Clock Frequency f
SCL
Standard mode (Note 10) 0 100
kHz
Fast mode (Note 10) 1.3
Bus Free Time Between STOP and
START Condition
t
BUF
Standard mode (Note 10) 4.7
µs
Fast mode (Notes 10, 11) 0.6
Hold Time (Repeated)
START Condition
Standard mode (Notes 10, 11) 4.0
µs
Fast mode (Note 10) 1.3
Low Period of SCL Clock t
LOW
Standard mode (Note 10) 4.7
µs
Fast mode (Note 10) 0.6
High Period of SCL Clock t
HIGH
Standard mode (Note 10) 4.0
µs
Fast mode (Notes 10, 12, 13) 0 0.9
Data Hold Time
Standard mode (Notes 10, 12, 13) 0
µs
Fast mode (Note 10)
Data Setup Time
Standard mode (Note 10)
ns
Fast mode (Note 10) 0.6
Start Setup Time
Standard mode (Note 10) 4.7
µs
Fast mode (Note 13)
300
Rise Time of Both SDA and SCL
Signals
t
F
Standard mode (Note 13)
ns
Fast mode (Note 13)
300
Fall Time of Both SDA and SCL
Signals
t
R
Standard mode (Note 13)
300
ns
Fast mode 0.6
Setup Time for STOP Condition
Standard mode 4.0
µs
Capacitive Load for Each Bus Line
C
B
(Note 13) 400 pF
EEPROM Write Time t
W
(Note 14) 10 ms
AC ELECTRICAL CHARACTERISTICS
(VCC= 3.0V to 5.5V, TA= -40°C to +95°C, unless otherwise noted.)
Note 1: All voltages are referenced to ground.
Note 2: I/O pins of fast-mode devices must not obstruct the SDA and SCL lines if V
CC
is switched off. The address inputs should be
connected to either V
CC
or GND depending on the desired address setting.
Note 3: SDA and SCL are connected to V
CC
and all other input signals are connected to well-defined logic levels.
Note 4: The maximum voltage the MON inputs will read is approximately 2.5V, even if the voltage on the inputs is greater than 2.5V.
Note 5: This voltage is defining the maximum range of the analog-to-digital converter and not the maximum V
CC
voltage.
Note 6: Absolute linearity is the difference of measured value from expected value at DAC position. The expected value is a
straight line from measured minimum position to measured maximum position.
Note 7: Relative linearity is the deviation of an LSB DAC setting change vs. the expected LSB change. The expected LSB change
is the slope of the straight line from measured minimum position to measured maximum position.
Note 8: See the Typical Operating Characteristics.
Note 9: The conversion accuracy does not include any error from the LM50.
Note 10: A fast-mode device can be used in a standard-mode system, but the requirement t
SU:DAT
> 250ns must then be met. This
is automatically the case if the device does not stretch the LOW period of the SCL signal. If such a device does stretch the
LOW period of the SCL signal, it must output the next data bit to the SDA line t
RMAX
+ t
SU:DAT
= 1000ns + 250ns = 1250ns
before the SCL line is released.
SYMBOL
MIN TYP MAX
t
HD:STA
t
HD:DAT
t
SU:DAT
t
SU:STA
t
SU:STO
100
250
20 + 0.1C
20 + 0.1C
20 + 0.1C
20 + 0.1C
B
B
B
B
1000
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
_____________________________________________________________________ 5
AC ELECTRICAL CHARACTERISTICS (continued)
(VCC= 3.0V to 5.5V, TA= -40°C to +95°C, unless otherwise noted.)
Note 11: After this period, the first clock pulse is generated.
Note 12: The maximum t
HD:DAT
only to has be met if the device does not stretch the LOW period (t
LOW
) of the SCL signal.
Note 13: A device must internally provide a hold time of at least 300ns for the SDA signal (see the V
IH MIN
of the SCL signal) in order
to bridge the undefined region of the falling edge of SCL.
Note 14: C
B
—total capacitance of one bus line, timing referenced to 0.9 x VCCand 0.1 x VCC.
Note 15: EEPROM write begins after a STOP condition occurs.
Typical Operating Characteristics
(VCC= 5.0V, TA= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
DS1857 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
806040200-20
540
580
620
660
700
500
-40 100
SUPPLY CURRENT vs. VOLTAGE
DS1857 toc02
VOLTAGE (V)
SUPPLY CURRENT (µA)
5.04.54.03.5
450
500
550
600
650
700
400
3.0 5.5
RESISTANCE vs. SETTING
DS1857 toc03
SETTING
RESISTANCE (kΩ)
25020015010050
10
20
30
40
50
60
0
0 300
ACTIVE SUPPLY CURRENT
vs. SCL FREQUENCY
DS1857 toc04
SCL FREQUENCY (kHz)
ACTIVE SUPPLY CURRENT (µA)
300200100
540
580
620
660
700
500
0 400
SDA = 5V
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
6 _____________________________________________________________________
Typical Operating Characteristics (continued)
(VCC= 5.0V, TA= +25°C, unless otherwise noted.)
RESISTOR 0 INL (LSB)
DS1857 toc05
POSITION
RESISTOR 0 INL (LSB)
225200150 17550 75 100 12525
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
-0.5
0 250
RESISTOR 0 DNL (LSB)
DS1857 toc06
RESISTOR 0 DNL (LSB)
-0.15
-0.05
0.05
0.15
0.25
-0.25
POSITION
225200150 17550 75 100 125250 250
RESISTOR 1 INL (LSB)
DS1857 toc07
POSITION
RESISTOR 1 INL (LSB)
225200150 17550 75 100 12525
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
-0.5
0 250
RESISTOR 1 DNL (LSB)
DS1857 toc08
RESISTOR 1 DNL (LSB)
-0.15
-0.05
0.05
0.15
0.25
-0.25
POSITION
225200150 17550 75 100 125250 250
EXTERNAL TEMP SENSOR VOLTAGE
vs. TEMPERATURE
DS1857 toc09
VOLTAGE (V)
TEMPERATURE (°C)
1.51.00.5
-20
0
20
40
60
80
100
120
140
-40
0 2.0
PPM vs. POSITION
DS1857 toc10
POSITION
ppm/°C
25020050 100 150
-10
40
90
140
190
240
290
340
-60
0 300
+25°C TO +85°C
+25°C TO -40°C
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
_____________________________________________________________________ 7
Detailed Description
The user can read the registers that monitor the VCC,
MON1, MON2, and temperature analog signals. After
each signal conversion, a corresponding bit is set that
can be monitored to verify that a conversion has
occurred. The signals also have alarm flags that notify
the user when the signals go above or below the userdefined value. Interrupts can also be set for each signal.
The position values of each resistor can be independently programmed. The user can assign a unique
value to each resistor for every 2°C increment over the
-40°C to +102°C range. Both resistors can also be put
in a high-impedance mode using the RHIZ pin.
An external temperature sense input, EXTTMP, converts an analog voltage into a digital value that represents temperature. Its scale is defined by +10mV/°C
gain and +500mV offset at 0°C. This corresponds to the
characteristics of the LM50 temperature sensor. The
resistor look-up tables are stepped through according
to this temperature every 2°C from -40°C to +102°C.
PIN
BALL
NAME
FUNCTION
1B2SDA 2-Wire Serial Data Interface. This pin is for serial data transfer to and from the device.
2A2SCL 2-Wire Serial Clock Interface. The serial clock input is used to clock data into and out of the device.
3C3A0Address Input. The address input pins specify the 2-wire address of the device (when ADFIX = 0).
4A1A1Address Input. The address input pins specify the 2-wire address of the device (when ADFIX = 0).
5B1A2Address Input. The address input pins specify the 2-wire address of the device (when ADFIX = 0).
6C2
Write Protect Enable. The device is not write protected if WPEN is connected to ground. This pin has
an internal pullup (R
WPEN
) (See Table 6).
7C1
Supply Ground
8D1
Resistor Disable Input. When high, this signal places both resistors in an off state or high impedance
mode. When low, the resistors are on. This pin has an internal pullup (R
RHIZ
).
9D3
External Analog Input
10 D4
External Analog Input
11 C4
External Temperature Input. This analog signal is converted into a digital value that represents a
temperature. The digitized value indexes through the look-up tables.
12 D2 L0
Low-End Resistor 0 Terminal. It is not required that the low-end terminals be connected to a potential
less than the high-end terminal of the corresponding resistor. Voltage applied to any of the resistor
terminals cannot exceed the power-supply voltage, VCC, or go below ground.
13 B3 H0
High-End Resistor 0 Terminal. It is not required that the high-end terminals be connected to a
potential greater than the low-end terminal of the corresponding resistor. Voltage applied to any of the
resistor terminals cannot exceed the power-supply voltage, VCC, or go below ground.
14 B4 L1 Low-End Resistor 1 Terminal
15 A4 H1 High-End Resistor 1 Terminal.
16 A3 V
CC
Supply Voltage
Pin Descriptions
WPEN
GND
RHIZ
MON1
MON2
EXTTMP
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
8 _____________________________________________________________________
DEVICE
ADDRESS
AD (AUXILIARY DEVICE ENABLE A0h)
MD (MAIN DEVICE ENABLE)
DEVICE ADDRESS
ADDRESS
ADDRESS
ADDRESS
R/W
R/W
DATA BUS
R/W
ADEN ADFIX
SDA
SCL
2-WIRE
INTERFACE
RHIZ
MON1
MON2
V
CC
GND
WPEN
EEPROM
128 x 8 BIT
00h-7Fh
STANDARDS
PROT
AUX
AD
ADDRESS
TABLE
SELECT
R/W
EEPROM
72 x 8 BIT
80h-C7h
TABLE 02
RESISTOR 0
LOOK-UP
TABLE
PROT
MAIN
MD
EEPROM
72 x 8 BIT
80h-C7h
SRAM
32 x 8 BIT
60h-7Fh
NOT PROTECTED
PROT
MAIN
MD
TEMP INDEX
ALARM FLAGS
MUX
CTRL
MEASUREMENT
ADDRESS
TABLE
SELECT
R/W
EEPROM
72 x 8 BIT
80h-C7h
TABLE 03
RESISTOR 1
LOOK-UP
TABLE
PROT
MAIN
MD
TEMP INDEX
V
CC
R
RHIZ
R
WPEN
MONITORS LIMIT
HIGH
MONITORS LIMIT
LOW
TABLE SELECT
TEMP INDEX
MINT (BIT)
EXTTMP
V
CC
MUX
A/D
12-BIT
A/D
CTRL
V
CC
V
CC
PROT AUX
PROT MAIN
MPEN
APEN
COMPARATOR
MEASUREMENT
ALARM FLAGS
MONITORS LIMIT LOW
MONITORS LIMIT HIGH
COMP CTRL
INTERRUPT
MINT
TABLE 01
EEPROM
16 x 8 BIT
80h-8Fh
VENDOR
PROT
MAIN
MD R/W
DEVICE ADDRESS
ADDRESS
TABLE SELECT
MASKING (TMP, V
CC
, MON1, MON2)
ADFIX (BIT)
ADEN (BIT)
MPEN (BIT)
APEN (BIT)
INV2 (BIT)
INV1 (BIT)
RHIZ
RESISTOR 0
50kΩ FULL SCALE
256 POSITIONS
L0
H0
REGISTERREGISTER
RHIZ
RESISTOR 1
50kΩ FULL SCALE
256 POSITIONS
L1
H1
A0
A1
A2
Figure 1. DS1857 Block Diagram
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
_____________________________________________________________________ 9
Monitored Signals
Each signal (VCC, MON1, MON2, and temperature) is
available as a 16-bit value with 12-bit accuracy (left-justified) over the serial bus. See Table 1 for signal scales
and Table 2 for signal format. The four LSBs should be
masked when calculating the value.
The signals are updated every frame rate (t
frame
) in a
round-robin fashion.
The comparison of all four signals with the high and low
user-defined values are done automatically. The corresponding flags are set to 1 within a specified time of
the occurrence of an out-of-limit condition.
Calculating Signal Values
The LSB = 100µV for V
CC
, and the LSB = 38.147µV for
the MON signals.
To calculate the value of VCC, convert the unsigned 16bit value to decimal and multiply by 100µV.
To calculate the value of MON1 or MON2, convert the
unsigned 16-bit value to decimal and multiply by
38.147µV.
To calculate the value of the temperature, treat the
two’s complement value binary number as an unsigned
binary number, then convert to decimal and divide by
256. If the result is greater than or equal to 128, then
subtract 256 from the result.
Temperature: high byte: -128°C to +127°C signed; low
byte: 1/256°C.
SIGNAL
+FS
+FS
-FS
-FS
(hex)
Temperature
-128°C 8000
V
CC
6.55V
0V 0000
MON1 2.5V
0V 0000
MON2 2.5V
0V 0000
Table 1. Scales for Monitor Channels
SIGNAL FORMAT
V
CC
Unsigned
MON1 Unsigned
MON2 Unsigned
Temperature Two’s complement
Table 2. Signal Comparison
TEMPERATURE
CORRESPONDING LOOK-UP
TABLE ADDRESS
<-40°C 80h
-40°C 80h
-38°C 81h
-36°C 82h
-34°C 83h
——
+98°C C5h
+100°C C6h
+102°C C7h
>+102°C C7h
Table 3. Look-up Table Address for
Corresponding Temperature Values
MSB
2
9
2
8
LSB 2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
Monitor VCCBit Weights
Temperature Bit Weights
Temperature Conversion Example
VCCConversion Example
Monitor Conversion Example
SIGNAL
127.996°C 7FFF
(hex)
FFFF
FFFF
FFFF
SIGNAL
15214213212211210
2
MSB (BIN) LSB (BIN) VOLTAGE (V)
11000000 00000000 1.875
10000000 10000000 1.255
S262
-1
2
2
5
4
2
-2
-3
2
-4
2
3
2
-5
2
2
2
-6
2
1
2
-7
2
0
2
-8
2
MSB (BIN) LSB (BIN) VOLTAGE (V)
10000000 10000000 3.29
11000000 11111000 4.94
MSB (BIN) LSB (BIN) TEMPERATURE (°C)
01000000 00000000 64
01000000 00001111 64.059
01011111 00000000 95
11110110 00000000 -10
11011000 00000000 -40
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
10 ____________________________________________________________________
ADEN
(ADDRESS
ENABLE)
NO. OF SEPARATE
DEVICE
ADDRESSES
ADDITIONAL
INFORMATION
02See Figure 2
1
See Figure 3
Table 4. ADEN Address Configuration
ADEN ADFIX
AUXILIARY
MAIN ADDRESS
00A0h *
01A0h
EEPROM
(Table 01, 8Ch)
10N/A *
11N/A
EEPROM
(Table 01, 8Ch)
Table 5. ADEN and ADFIX Bits
MAIN
DEVICE
MON LOOK-UP
TABLE CONTROL
R0 LOOK-UP
TABLE
AUXILIARY
DEVICE
0
DEC
0
95
96
127
128
143
199
MEMORY PARTITION WITH ADEN BIT = 0
EN
EN
EN
EN
SEL
EN
SEL
7Fh 7Fh
80h
80h
60h
C7h
F0h
FFh
RESERVED RESERVED
8Fh
5Fh
TABLE SELECT
MAIN DEVICE ENABLE
AUXILIARY DEVICE ENABLE
DECODER
0
F0h
FFh
R1 LOOK-UP
TABLE
EN
SEL
80h
C7h
TABLE 03TABLE 02TABLE 01
Figure 2. Memory Organization, ADEN = 0
MAIN
DEVICE
MON LOOK-UP
TABLE CONTROL
R0 LOOK-UP
TABLE
AUXILIARY
DEVICE
80h
DEC
0
95
96
127
128
143
199
255
EN
EN
EN
EN
SEL
EN
SEL
FFh
7Fh
80h
80h
C7h
F0h
FFh
RESERVED RESERVED
8Fh
TABLE SELECT
TABLE 00
MAIN DEVICE ENABLE
DECODER
0
F0h
FFh
R1 LOOK-UP
TABLE
EN
SEL
80h
C7h
TABLE 03TABLE 02TABLE 01
MEMORY PARTITION WITH ADEN BIT = 1
60h
5Fh
Figure 3. Memory Organization, ADEN = 1
*
1 (Main Device only)
ADDRESS
1010A2A1A0R/W
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
____________________________________________________________________ 11
Variable Resistors
The value of each variable resistor is determined by a
temperature-addressed look-up table, which can
assign a unique value (00h to FFh) to each resistor for
every 2°C increment over the -40°C to +102°C range
(see Table 3). See the Temperature Conversion section
for more information.
A resistor disable feature places both outputs in a highimpedance mode. This occurs when the RHIZ input is
high. An internal pullup of R
RHIZ
is provided, readying
this pin for input from the Tx Disable signal as specified
in the SFF and SFP MSA.
The variable resistors can also be used in manual
mode. If the TEN bit equals 0, then the resistors are in
manual mode and the temperature indexing is disabled. The user sets the resistors in manual mode by
writing to addresses 82h and 83h in Table 01 to control
resistors 0 and 1, respectively.
Memory Description
Main and auxiliary memories can be accessed by two
separate device addresses. The Main Device address
is determined by address pins or value in Table 01 byte
8Ch, when ADFIX = 1 (see Table 5). The Auxiliary
Device address is A0h. A user option is provided to
respond to one or two device addresses. This feature
can be used to save component count in SFF applications (Main Device address can be used) or other
applications where both GBIC (Auxiliary Device
address can be used) and monitoring functions are
implemented and two device addresses are needed.
The memory blocks are enabled with the corresponding device address. Memory space from 80h and up is
accessible only through the Main Device address. This
memory is organized as three tables; the desired table
can be selected by the contents of memory location
7Fh, Main Device. The Auxiliary Device address has no
access to the tables, but the Auxiliary Device address
can be mapped into the Main Device’s memory space
as a fourth table. Device addresses are programmable
with two control bits in EEPROM.
ADEN configures memory access to respond to different device addresses (see Tables 4 and 5).
The default device address for EEPROM-generated
addresses is A2h.
If the ADEN bit is 1, additional 128 bytes of EEPROM
are accessible through the Main Device, selected as
Table 00 (see Figure 3). In this configuration, the
Auxiliary Device address is not accessible. APEN controls the direction of Table 00 regardless of the setting
of ADEN.
ADFIX (address fixed) determines whether the Main
Device address is determined by an EEPROM byte
(Table 01, byte 8Ch, when ADFIX =1). There can be up
to 128 devices sharing a common 2-wire bus, with
each device having its own unique device address.
Memory Protection
Memory access from either device address can be
either read/write or read only. Write protection is
accomplished by a combination of control bits in
EEPROM (APEN and MPEN in configuration register
89h) and a write-protect enable (WPEN) pin. Since the
WPEN pin is often not accessible from outside the module, this scheme effectively allows the module to be
locked by the manufacturer to prevent accidental writes
by the end user.
Separate write protection is provided for the Auxiliary
and Main Device address through distinct bits APEN
and MPEN. APEN and MPEN are bits from configuration register 89h, Table 01. Due to the location, the
APEN and MPEN bits can only be written through the
Main Device address. The control of write privileges
through the Auxiliary Device address is dependent on
the value of APEN. Care should be taken with the setting of MPEN, once set to a 1, assuming WPEN is high,
access through the Main Device is thereafter denied
unless WPEN is taken to a low level. By this means
inadvertent end-user write access can be denied.
Main Device address space 60h to 7Fh is SRAM and is
not write protected by APEN, MPEN, or WPEN. For
example, the user may reset flags set by the device.
Bytes designated as “Reserved” may be used as
scratchpad but they will not be stored in a power cycle
because of their volatility. These bytes are reserved for
added functionality in future versions of this device.
Note that in single device mode (ADEN bit = 1), APEN
determines the protection level of Table 00, independent of WPEN.
The write-protect operation, for both Main and Auxiliary
Devices, is summarized in Tables 6 and 7.
WPEN
MPEN PROTECT MAIN
0X No
X0 No
11 Yes
Table 6. Main Device
APEN
WPEN PROTECT AUXILIARY
0
XNo
1
X Yes
Table 7. Auxiliary Device
DS1857
Register Map
A description of the registers is below. The registers
are read only (R) or read/write (R/W). The R/W registers
are writable only if write protect has not been asserted
(see the Memory Description section).
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
12 ____________________________________________________________________
MEMORY LOCATION
(hex)
EEPROM/SRAM
R/W
DEFAULT SETTING
(hex)
NAME OF LOCATION FUNCTION
00 to 7F EEPROM
R/W
00 Standards Data —
Auxiliary Device
MEMORY
LOCATION
(hex)
EEPROM/
SRAM
DEFAULT
(hex)
FUNCTION
00 to 01 EEPROM
00
byte 70h is set.
02 to 03 EEPROM
00
70h is set.
04 to 07 EEPROM R 00 Reserved —
08 to 09 EEPROM
00
is set.
0A to 0B EEPROM
00
is set.
0C to 0F EEPROM — 00 Reserved —
10 to 11 EEPROM
00
is set.
12 to 13 EEPROM
00
is set.
14 to 17 EEPROM — 00 Reserved —
18 to 19 EEPROM
00
is set.
1A to 1B EEPROM
00
is set.
Main Device
Note: SRAM defaults are power-on defaults. EEPROM defaults are factory defaults.
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
SETTING
NAME OF LOCATION
Contains upper limit settings for temperature.
TMPlimhi (MSB to LSB)
TMPlimlo (MSB to LSB)
VCClimhi (MSB to LSB)
VCClimlo (MSB to LSB)
MON1limhi (MSB to LSB)
MON1limlo (MSB to LSB)
MON2limhi (MSB to LSB)
MON2limlo (MSB to LSB)
If the limit is violated, a flag in Main Device
Contains lower limit settings for temperature. If
the limit is violated, a flag in Main Device byte
Contains upper limit settings for V
limit is violated, a flag in Main Device byte 70h
Contains lower limit settings for V
limit is violated, a flag in Main Device byte 70h
Contains upper limit settings for MON1. If the
limit is violated, a flag in Main Device byte 70h
Contains lower limit settings for MON1. If the
limit is violated, a flag in Main Device byte 70h
Contains upper limit settings for MON2. If the
limit is violated, a flag in Main Device byte 70h
Contains lower limit settings for MON2. If the
limit is violated, a flag in Main Device byte 70h
CC
CC
. If the
. If the
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
____________________________________________________________________ 13
MEMORY
LOCATION
(hex)
EEPROM/
SRAM
R/W
DEFAULT
(hex)
NAME OF LOCATION
FUNCTION
1C to 5F EEPROM — 00 Reserved —
60 to 61 SRAM R —
Measured TMP
(MSB to LSB)
Digitized measured value for temperature.
See Table 1.
62 to 63 SRAM R —
Measured V
CC
(MSB to LSB)
Digitized measured value for V
CC
.
See Table 1.
64 to 65 SRAM R —
Measured MON1
(MSB to LSB)
Digitized measured value for MON1.
See Table 1.
66 to 67 SRAM R —
Measured MON2
(MSB to LSB)
Digitized measured value for MON2.
See Table 1.
68 to 6D SRAM R — Reserved —
6E SRAM — — Logic states —
Bit 7 — R X HIZSTA
Resistor status bit. A high indicates that both
resistors are in high-impedance mode. A low
indicates that both resistors are operating
normally.
6—
0 HIZCO
Resistor control bit. Setting this bit high
causes both resistors to go into a highimpedance state.
5——X X —
4——X X —
3——X X —
2——X X —
1——X X —
0—RX RDYB
This status bit goes high when VCC has fallen
below the POA level.
6F SRAM — — Conversion updates —
Bit 7 —
0 TAU
This bit goes high after a temperature and
address update has occurred for the
corresponding measurement in bytes 60h to
61h. This bit can be written to a 0 by the user
and monitored to verify that a conversion has
occurred.
Main Device (continued)
SETTING
R/W
R/W
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
14 ____________________________________________________________________
MEMORY
LOCATION
(hex)
EEPROM/
SRAM
DEFAULT
(hex)
FUNCTION
6—
0V
CC
U
conversion has occurred.
5—
0 MON1U
conversion has occurred.
4—
0 MON2U
conversion has occurred.
3——0 0 —
2——0 0 —
1——0 X —
0——0 X —
70 SRAM R — Alarm flags —
Bit 7 — — — TMPhi
of the temperature setting is violated.
6——— TMPlo
of the temperature setting is violated.
5——— V
CC
hi
of the VCC setting is violated.
Main Device (continued)
R/W
R/W
R/W
R/W
SETTING
NAME OF LOCATION
This bit goes high after a VCC update has
occurred for the corresponding measurement
in bytes 62h to 63h. This bit can be written to
a 0 by the user and monitored to verify that a
This bit goes high after a MON1 update has
occurred for the corresponding measurement
in bytes 64h to 65h. This bit can be written to
a 0 by the user and monitored to verify that a
This bit goes high after a MON2 update has
occurred for the corresponding measurement
in bytes 66h to 67h. This bit can be written to
a 0 by the user and monitored to verify that a
This alarm flag goes high when the upper limit
This alarm flag goes high when the lower limit
This alarm flag goes high when the upper limit
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
____________________________________________________________________ 15
MEMORY
LOCATION
(hex)
EEPROM/
SRAM
R/W
DEFAULT
(hex)
NAME OF LOCATION
FUNCTION
4——— V
CC
lo
This alarm flag goes high when the lower limit
of the VCC setting is violated.
3——— MON1hi
This alarm flag goes high when the upper limit
of the MON1 setting is violated.
2——— MON1lo
This alarm flag goes high when the lower limit
of the MON1 setting is violated.
1——— MON2hi
This alarm flag goes high when the upper limit
of the MON2 setting is violated.
0——— MON2lo
This alarm flag goes high when the lower limit
of the MON2 setting is violated.
71 SRAM R — Alarm flags —
Bit 7 — — — X —
6——— X —
5——— X —
4——— X —
3——— X —
2——— X —
1——— X —
0——— MINT
A mask of all flags located in Table 01 byte
88h determines the value of MINT. MINT is
maskable to 0 if no interrupt is desired by
setting Table 01 byte 88h to 0.
72 to 7E SRAM R 00 Reserved —
7F SRAM
Table select —
Bit 7 — — 0 X —
6——0 X —
5——0 X —
4——0 X —
3——0 X —
2——0 X —
1——0
0——0
Table select bits
Set bits = 00 to select Table 00, set bits = 01
to select Table 01, set bits = 10 to select
Table 02, set bits = 11 to select Table 03.
Main Device (continued)
SETTING
R/W
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
16 ____________________________________________________________________
MEMORY
LOCATION
(hex)
EEPROM/
SRAM
R/W
DEFAULT
SETTING
(hex)
NAME OF
LOCATION
FUNCTION
80 SRAM R/W Mode —
Bit 7 — — 0 X —
6——0 X —
5——0 X —
4——0 X —
3——0 X —
2——0 X —
1——1 TEN
If TEN = 0, the temperature conversions update and the
resistors can be controlled manually. The user sets the
resistor in manual mode by writing to addresses 82h and
83h in Table 01 to control resistors 0 and 1, respectively.
0——1 AEN
AEN = 0 provides manual control of the temperature
index.
81 SRAM R — Temp index
This byte is the temperature-calculated index used to
select the address of resistor settings in the look-up
tables.
82
SRAM R/W 00 Resistor 0 Resistor 0 position values from 00h to FFh.
83
SRAM R/W 00 Resistor 1 Resistor 1 position values from 00h to FFh.
84 to 87 SRAM — 00 Reserved —
88
R/W X X —
Bit 7 — — 1 TMP —
6——1 V
CC
—
5——1 MON1 —
4——1 MON2 —
3——0 X —
2——0 X —
1——0 X —
0——0 X —
89
R/W — Configuration —
Bit 7 — — 0 X —
6——0 X —
Table 01h
EEPROM
EEPROM
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
____________________________________________________________________ 17
MEMORY
LOCATION
(hex)
EEPROM/
SRAM
R/W
DEFAULT
SETTING
(hex)
NAME OF
LOCATION
FUNCTION
5——0 ADEN
Table 5).
4——0 ADFIX
and Table 5).
3——0 APEN
C ontr ol s auxi l i ar y w r i te p r otect. S ee the M em or y D escr i p ti on
2——0 MPEN
C ontr ol s auxi l i ar y w r i te p r otect. S ee the M em or y D escr i p ti on
1——0 X —
0——0 X —
8A to 8B
—00 Reserved —
8C
R/W A2
ADFIX = 0, then address pins determine the address.
8D to 8F
—— Reserved —
Table 01h (continued)
MEMORY
LOCATION
(hex)
EEPROM/
SRAM
R/W
DEFAULT
(hex)
NAME OF LOCATION FUNCTION
80 to C7
R/W FF Resistor 0 Temp LUT Look-up table for Resistor 0.
F0 to FF
RFF Reserved —
Table 02h
MEMORY
LOCATION
(hex)
EEPROM/
SRAM
R/W
DEFAULT
SETTING
(hex)
NAME OF LOCATION FUNCTION
80 to C7
R/W FF Resistor 1 Temp LUT Look-up table for Resistor 1.
F0 to FF
RFF Reserved —
Table 03h
EEPROM
EEPROM
EEPROM
Device address
Controls if the device responds to one or two device
addresses (see the Memory Description section and
Controls the means by which Main and Auxiliary Device
addresses are set (see the Memory Description section
Contains Main Device address if the bit ADFIX = 1. If
SETTING
EEPROM
EEPROM
EEPROM
EEPROM
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
18 ____________________________________________________________________
Temperature Conversion
Temperature is sensed from an external sensor. The sensor’s scale is +10mV/°C for gain and +500mV for offset at
0°C. The DS1857 accommodates a temperature range of
-40°C to 102°C for its look-up tables. The resistor look-up
tables are stepped through according to this temperature
every 2°C. The relationship between the voltage and temperature is shown in Equation 2.
The direct-to-digital temperature sensor measures temperature through the use of an on-chip temperature
measurement technique with an operating range from
-40°C to +102°C. Temperature conversions are initiated
upon power-up, and the most recent conversion is
stored in memory locations 60h and 61h of the Main
Device, which are updated every t
frame
. Temperature
conversions do not occur during an active read or write
to memory.
The value of each resistor is determined by the temperature-addressed look-up table. The look-up table assigns
a unique value to each resistor for every 2°C increment
with a 1°C hysteresis at a temperature transition over the
operating temperature range (see Figure 4).
Power-Up and Low Voltage Operation
During power-up, the device is inactive until VCC
exceeds the digital power-on-reset voltage (POD). At
this voltage, the digital circuitry, which includes the 2wire interface, becomes functional. However, EEPROM
backed registers/settings cannot be internally read
(recalled into shadow SRAM) until VCCexceeds the
analog power-on-reset voltage (POA) at which time the
remainder of the device becomes fully functional. Once
VCC exceeds POA, the RDYB bit in byte 6Eh of the
Main Device memory is timed to go from a 1 to a 0 and
indicates when analog to digital conversions begin. If
VCC ever dips below POA, the RDYB bit will read as a
1 again. Once a device exceeds POA and the EEPROM is recalled, the values remain active (recalled)
until VCCfalls below POD.
For 2-wire device addresses sourced from EEPROM
(ADFIX = 1), the device address defaults to the
address determined by the address pins until V
CC
exceeds POA and the EEPROM values are recalled.
The Auxiliary Device (A0h) is always available within
this voltage window (between POD and the EEPROM
recall) regardless of the programmed state of ADEN.
Furthermore, as the device powers-up, the VCClo alarm
flag (bit 4 of 70h in Main Device) will default to a 1 until
the first VCCanalog-to-digital conversion occurs and
sets or clears the flag accordingly.
2-Wire Operation
Clock and Data Transitions: The SDA pin is normally
pulled high with an external resistor or device. Data on
the SDA pin may only change during SCL-low time
periods. Data changes during SCL-high periods will
indicate a start or stop condition depending on the conditions discussed below. See the timing diagrams in
Figures 5 and 6 for further details.
Start Condition: A high-to-low transition of SDA with
SCL high is a start condition, which must precede any
other command. See the timing diagrams in Figures 5
and 6 for further details.
Stop Condition: A low-to-high transition of SDA with
SCL high is a stop condition. After a read or write
sequence, the stop command places the DS1857 into a
low-power mode. See the timing diagrams in Figures 5
and 6 for further details.
Acknowledge: All address and data bytes are transmitted through a serial protocol. The DS1857 pulls the
SDA line low during the ninth clock pulse to acknowledge that it has received each word.
Standby Mode: The DS1857 features a low-power
mode that is automatically enabled after power-on,
after a stop command, and after the completion of all
internal operations.
Device Addressing: The DS1857 must receive an 8-bit
device address word following a start condition to enable
a specific device for a read or write operation. The
address word is clocked into this part’s MSB to LSB. The
address byte consists of Ah (1010) followed by the value
of the address pins (A1, A2, and A0)then the R/W bit. This
T
VV
mV
=
− 05
10
.
(1)
M6
M5
M4
M3
M2
M1
246810 12
TEMPERATURE (°C)
MEMORY LOCATION
INCREASING
TEMPERATURE
DECREASING
TEMPERATURE
Figure 4. Look-Up Table Temperature Hysteresis
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
____________________________________________________________________ 19
byte must match the address programmed into Table 01
8Ch or A0h (for the Auxiliary Device). If a device address
match occurs, this part will output a zero for one clock
cycle as an acknowledge and the corresponding block of
memory is enabled (see the Memory Organization section). If the R/W bit is high, a read operation is initiated. If
the R/W is low, a write operation is initiated (see the
Memory Organization section). If the address does not
match, this part returns to a low-power mode.
Write Operations
After receiving a matching address byte with the R/W
bit set low, provided there is no write protect, the
device goes into the write mode of operation (see the
Memory Organization section). The master must transmit an 8-bit EEPROM memory address to the device to
define the address where the data is to be written. After
the byte has been received, the DS1857 transmits a
zero for one clock cycle to acknowledge the address
has been received. The master must then transmit an
8-bit data word to be written into this address. The
DS1857 again transmits a zero for one clock cycle to
acknowledge the receipt of the data. At this point, the
master must terminate the write operation with a stop
condition. The DS1857 then enters an internally timed
write process twto the EEPROM memory. All inputs are
disabled during this byte write cycle.
Page Write
The DS1857 is capable of an 8-byte page write. A page
is any 8-byte block of memory starting with an address
evenly divisible by eight and ending with the starting
address plus seven. For example, addresses 00h
through 07h constitute one page. Other pages would
be addresses 08h through 0Fh, 10h through 17h, 18h
through 1Fh, etc.
A page write is initiated the same way as a byte write,
but the master does not send a STOP condition after
the first byte. Instead, after the slave acknowledges the
data byte has been received, the master can send up
to seven more bytes using the same nine-clock
sequence. The master must terminate the write cycle
with a STOP condition or the data clocked into the
DS1857 will not be latched into permanent memory.
The address counter rolls on a page during a write. The
counter does not count through the entire address
space as during a read. For example, if the starting
address is 06h and 4 bytes are written, the first byte
goes into address 06h. The second goes into address
07h. The third goes into address 00h (not 08h). The
fourth goes into address 01h. If more than 9 bytes or
more are written before a STOP condition is sent, the
first bytes sent are overwritten. Only the last 8 bytes of
data are written to the page.
Acknowledge Polling: Once the internally timed write
has started and the DS1857 inputs are disabled,
acknowledge polling can be initiated. The process
involves transmitting a start condition followed by the
device address. The R/W bit signifies the type of operation that is desired. The read or write sequence will only
be allowed to proceed if the internal write cycle has
completed and the DS1857 responds with a zero.
Read Operations
After receiving a matching address byte with the R/W bit
set high, the device goes into the read mode of operation. There are three read operations: current address
read, random read, and sequential address read.
Current Address Read
The DS1857 has an internal address register that maintains the address used during the last read or write
operation, incremented by one. This data is maintained
as long as VCCis valid. If the most recent address was
the last byte in memory, then the register resets to the
first address.
Once the device address is clocked in and acknowledged by the DS1857 with the R/W bit set to high, the
current address data word is clocked out. The master
does not respond with a zero, but does generate a stop
condition afterwards.
Single Read
A random read requires a dummy byte write sequence to
load in the data byte address. Once the device and data
address bytes are clocked in by the master, and
acknowledged by the DS1857, the master must generate
another start condition. The master now initiates a current
address read by sending the device address with the
R/W bit set high. The DS1857 acknowledges the device
address and serially clocks out the data byte.
Sequential Address Read
Sequential reads are initiated by either a current
address read or a random address read. After the master receives the first data byte, the master responds
with an acknowledge. As long as the DS1857 receives
this acknowledge after a byte is read, the master can
clock out additional data words from the DS1857. After
reaching address FFh, it resets to address 00h.
The sequential read operation is terminated when the
master initiates a stop condition. The master does not
respond with a zero.
For a more detailed description of 2-wire theory of
operation, see the following section.
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
20 ____________________________________________________________________
2-Wire Serial Port Operation
The 2-wire serial port interface supports a bidirectional
data transmission protocol with device addressing. A
device that sends data on the bus is defined as a transmitter, and a device receiving data as a receiver. The
device that controls the message is called a master.
The devices that are controlled by the master are
slaves. The bus must be controlled by a master device
that generates the serial clock (SCL), controls the bus
access, and generates the start and stop conditions.
The DS1857 operates as a slave on the 2-wire bus.
Connections to the bus are made through the opendrain I/O lines SDA and SCL. The following I/O terminals control the 2-wire serial port: SDA, SCL. Timing
diagrams for the 2-wire serial port can be found in
Figures 5 and 6. Timing information for the 2-wire serial
port is provided in the AC Electrical Characteristics
table for 2-wire serial communications.
The following bus protocol has been defined:
• Data transfer may be initiated only when the bus is
not busy.
• During data transfer, the data line must remain
stable whenever the clock line is high. Changes in
the data line while the clock line is high will be
interpreted as control signals.
Accordingly, the following bus conditions have been
defined:
Bus not busy: Both data and clock lines remain high.
Start data transfer: A change in the state of the data
line from high to low while the clock is high defines a
start condition.
Stop data transfer: A change in the state of the data
line from low to high while the clock line is high defines
the stop condition.
Data valid: The state of the data line represents valid
data when, after a start condition, the data line is stable
for the duration of the high period of the clock signal. The
data on the line can be changed during the low period of
the clock signal. There is one clock pulse per bit of data.
Figures 5 and 6 detail how data transfer is accomplished
on the 2-wire bus. Depending upon the state of the R/W
bit, two types of data transfer are possible.
Each data transfer is initiated with a start condition and
terminated with a stop condition. The number of data
bytes transferred between start and stop conditions is
not limited and is determined by the master device. The
information is transferred byte-wise and each receiver
acknowledges with a ninth bit.
Within the bus specifications a regular mode (100kHz
clock rate) and a fast mode (400kHz clock rate) are
defined. The DS1857 works in both modes.
Acknowledge: Each receiving device, when
addressed, is obliged to generate an acknowledge
after the byte has been received. The master device
must generate an extra clock pulse which is associated
with this acknowledge bit.
A device that acknowledges must pull down the SDA
line during the acknowledge clock pulse in such a way
that the SDA line is a stable low during the high period
of the acknowledge related clock pulse. Setup and
hold times must be taken into account. A master must
signal an end of data to the slave by not generating an
acknowledge bit on the last byte that has been clocked
out of the slave. In this case, the slave must leave the
data line high to enable the master to generate the stop
condition.
1) Data transfer from a master transmitter to a slave
receiver. The first byte transmitted by the master is
the command/control byte. Next follows a number
of data bytes. The slave returns an acknowledge
bit after each received byte.
2) Data transfer from a slave transmitter to a master
receiver. The master transmits the first byte (the
command/control byte) to the slave. The slave
then returns an acknowledge bit. Next follows a
number of data bytes transmitted by the slave to
the master. The master returns an acknowledge
bit after all received bytes other than the last byte.
At the end of the last received byte, a not
acknowledge can be returned.
The master device generates all serial clock pulses and
the start and stop conditions. A transfer is ended with a
stop condition or with a repeated start condition. Since
a repeated start condition is also the beginning of the
next serial transfer, the bus will not be released.
The DS1857 can operate in the following three modes:
1) Slave Receiver Mode: Serial data and clock are
received through SDA and SCL, respectively.
After each byte is received, an acknowledge bit is
transmitted. Start and stop conditions are recognized as the beginning and end of a serial transfer. Address recognition is performed by hardware
after the slave (device) address and direction bit
have been received.
2) Slave Transmitter Mode: The first byte is
received and handled as in the slave receiver
mode. However, in this mode the direction bit indicates that the transfer direction is reversed. Serial
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
____________________________________________________________________ 21
data is transmitted on SDA by the DS1857, while
the serial clock is input on SCL. Start and stop
conditions are recognized as the beginning and
end of a serial transfer.
3) Slave Address: Command/control byte is the first
byte received following the start condition from the
master device. The command/control byte consists of a 4-bit control code. For the DS1857, this
is set as 1010 binary for read/write operations. The
next three bits of the command/control byte are
the device select bits or device address. They are
used by the master device to select which of eight
possible devices on the bus is to be accessed.
When reading or writing the DS1857, the deviceselect bits must match one of two valid device
addresses 00h, or the address registered in Table
01 location 8Ch. The last bit of the command/control byte (R/W) defines the operation to be performed. When set to a ‘1’ a read operation is
selected, and when set to a ‘0’ a write operation is
selected. The slave address can be set by the
EEPROM.
Following the start condition, the DS1857 monitors the
SDA bus checking the device type identifier being
transmitted. Upon receiving the 1010 control code, the
appropriate device address bits, and the read/write bit,
the slave device outputs an acknowledge signal on the
SDA line.
Chip Topology
TRANSISTOR COUNT: 44149
SUBSTRATE CONNECTED TO GROUND.
STOP
CONDITION
OR REPEATED
START
CONDITION
REPEATED IF MORE BYTES
ARE TRANSFERRED
ACK
START
CONDITION
ACK
ACKNOWLEDGEMENT
SIGNAL FROM RECEIVER
ACKNOWLEDGEMENT
SIGNAL FROM RECEIVER
SLAVE ADDRESS
MSB
SCL
SDA
R/W
DIRECTION
BIT
12 678 9 12 8 93–7
Figure 5. 2-Wire Data Transfer Protocol
DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
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© 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
SDA
SCL
t
HD:STA
t
LOW
t
HIGH
t
R
t
F
t
BUF
t
HD:DAT
t
SU:DAT
REPEATED
START
t
SU:STA
t
HD:STA
t
SU:STO
t
SP
STOP START
Figure 6. 2-Wire AC Characteristics
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