MC145192 MOTOROLA
8
PIN DESCRIPTIONS
DIGITAL INTERFACE PINS
Data In (Pin 19)
Serial Data Input. The bit stream begins with the MSB and
is shifted in on the low–to–high transition of Clock. The bit
pattern is 1 byte (8 bits) long to access the C or configuration
register, 2 bytes (16 bits) to access the first buffer of the R
register, or 3 bytes (24 bits) to access the A register (see
Table 1). The values in the C, R, and A registers do not
change during shifting because the transfer of data to the
registers is controlled by Enable
.
CAUTION
The value programmed for the N–counter must
be greater than or equal to the value of the A–
counter.
The 13 LSBs of the R register are double–buffered. As indicated above, data is latched into the first buffer on a 16–bit
transfer. (The 3 MSBs are not double–buffered and have an
immediate effect after a 16–bit transfer .) The second buffer of
the R register contains the 13 bits for the R counter. This second buffer is loaded with the contents of the first buffer when
the A register is loaded (a 24–bit transfer). This allows presenting new values to the R, A, and N counters simultaneously. If this is not required, then the 16–bit transfer may
be followed by pulsing Enable
low with no signal on the Clock
pin. This is an alternate method of transferring data to the
second buffer of the R register. See Figure 17.
The bit stream needs neither address nor steering bits due
to the innovative BitGrabber registers. Therefore, all bits in
the stream are available to be data for the three registers.
Random access of any register is provided. That is, the registers may be accessed in any sequence. Data is retained in
the registers over a supply range of 2.7 to 5.0 V . The formats
are shown in Figures 15, 16, and 17.
Data In typically switches near 50% of VDD to maximize
noise immunity. This input can be directly interfaced to
CMOS devices with outputs guaranteed to switch near rail–
to–rail. When interfacing to NMOS or TTL devices, either a
level shifter (MC74HC14A, MC14504B) or pull–up resistor of
1kΩ to 10 kΩ must be used. Parameters to consider when
sizing the resistor are worst–case IOL of the driving device,
maximum tolerable power consumption, and maximum data
rate.
Table 1. Register Access
(MSBs are shifted in first, C0, R0, and A0 are the LSBs)
Number
of Clocks
Accessed
Register
Bit
Nomenclature
8
16
24
Other Values ≤ 32
Values > 32
C Register
R Register
A Register
Not Allowed
See Figures 24
to 27
C7, C6, C5, . . ., C0
R15, R14, R13, . . ., R0
A23, A22, A21, . . ., A0
Clock (Pin 18)
Serial Data Clock Input. Low–to–high transitions on Clock
shift bits available at the Data pin, while high–to–low transitions shift bits from Output A (when configured as Data Out,
see Pin 16). The 24–1/2–stage shift register is static,
allowing clock rates down to dc in a continuous or intermittent mode.
Eight clock cycles are required to access the C register.
Sixteen clock cycles are needed for the first buffer of the R
register. Twenty–four cycles are used to access the A register. See Table 1 and Figures 15, 16, and 17. The number of
clocks required for cascaded devices is shown in Figures 25
through 27.
Clock typically switches near 50% of VDD and h as a
Schmitt–triggered input buffer. Slow Clock rise and fall times
are allowed. See the last paragraph of Data In for more
information.
NOTE
To guarantee proper operation of the power–on
reset (POR) circuit, the Clock pin must be held at
GND (with Enable
being a don’t care) or Enable
must be held at the potential of the V+ pin (with
Clock being a don’t care) during power–up. As an
alternative, the bit sequence of Figure 18 may be
used.
Enable
(Pin 17)
Active–Low Enable Input. This pin is used to activate the
serial interface to allow the transfer of data to/from the device. When Enable is in an inactive high state, shifting is inhibited and the port is held in the initialized state. To transfer
data to the device, Enable
(which must start inactive high) is
taken low, a serial transfer is made via Data In and Clock,
and Enable
is taken back high. The low–to–high transition on
Enable transfers data to the C or A registers and first buffer
of the R register, depending on the data stream length per
Table 1.
NOTE
Transitions on Enable
must not be attempted
while Clock is high. This will put the device out of
synchronization with the microcontroller. Resynchronization occurs when Enable
is high and
Clock is low.
This input is also Schmitt–triggered and switches near
50% of VDD, thereby minimizing the chance of loading erroneous data into the registers. See the last paragraph of Data
In for more information.
For POR information, see the note for the Clock pin.
Output A (Pin 16)
Configurable Digital Output. Output A is selectable as fR,
fV, Data Out, or Port. Bits A22 and A23 in the A register control the selection; see Figure 16.
If A23 = A22 = high, Output A is configured as fR. This signal is the buffered output of the 13–stage R counter. The f
R
signal appears as normally low and pulses high. The fR signal can be used to verify the divide ratio of the R counter.
This ratio extends from 5 to 8191 and is determined by the
binary value loaded into bits R0 through R12 in the R register. Also, direct access to the phase detectors via the REF
in
pin is allowed by choosing a divide value of one. See Figure 17. The maximum frequency at which the phase detectors operate is 1 MHz. Therefore, the frequency of fR should
not exceed 1 MHz.
If A23 = high and A22 = low, Output A is configured as fV.
This signal is the buffered output of the 12–stage N counter.