Texas Instruments SN74ABT3613-20PCB, SN74ABT3613-20PQ, SN74ABT3613-30PCB, SN74ABT3613-30PQ, SN74ABT3613-15PCB Datasheet
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SN74ABT3613
64 × 36 CLOCKED FIRST-IN, FIRST-OUT MEMORY
WITH BUS MATCHING AND BYTE SWAPPING
SCBS128F – JULY 1992 – REVISED APRIL 1998
1
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
D
Low-Power Advanced BiCMOS Technology
D
Free-Running CLKA and CLKB Can Be
Asynchronous or Coincident
D
64 × 36 FIFO Buffering Data From Port A to
Port B
D
Mailbox-Bypass Registers in Each
Direction
D
Dynamic Port-B Bus Sizing of 36 Bits (Long
Word), 18 Bits (Word), and 9 Bits (Byte)
D
Selection of Big- or Little-Endian Format for
Word and Byte Bus Sizes
D
Three Modes of Byte-Order Swapping on
Port B
D
Programmable Almost-Full and
Almost-Empty Flags
D
Microprocessor Interface Control Logic
D
FF and AF Flags Synchronized by CLKA
D
EF and AE Flags Synchronized by CLKB
D
Passive Parity Checking on Each Port
D
Parity Generation Can Be Selected for Each
Port
D
Supports Clock Frequencies up to 67 MHz
D
Fast Access Times of 10 ns
D
Package Options Include 120-Pin Thin
Quad Flat (PCB) and 132-Pin Quad Flat
(PQ) Packages
description
The SN74ABT3613 is a high-speed, low-power BiCMOS clocked FIFO memory . It supports clock frequencies
up to 67 MHz and has read-access times as fast as 10 ns. A 64 × 36 dual-port SRAM FIFO in this device buffers
data from port A to port B. The FIFO has flags to indicate empty and full conditions and two programmable flags
(almost full and almost empty) to indicate when a selected number of words is stored in memory . FIFO data on
port B can be output in 36-bit, 18-bit, and 9-bit formats, with a choice of big- or little-endian configurations. Three
modes of byte-order swapping are possible with any bus-size selection. Communication between each port can
bypass the FIFO via two 36-bit mailbox registers. Each mailbox register has a flag to signal when new mail has
been stored. Parity is checked passively on each port and can be ignored if not desired. Parity generation can
be selected for data read from each port.
The SN74ABT3613 is a clocked FIFO, which means each port employs a synchronous interface. All data
transfers through a port are gated to the low-to-high transition of a continuous (free-running) port clock by enable
signals. The continuous clocks for each port are independent of one another and can be asynchronous or
coincident. The enables for each port are arranged to provide a simple interface between microprocessors
and/or buses controlled by a synchronous interface.
The full flag (FF
) and almost-full (AF) flag of a FIFO are two-stage synchronized to the port clock that writes data
to its array . The empty flag (EF
) and almost-empty (AE) flag of a FIFO are two-stage synchronized to the port
clock that reads data from its array.
The SN74ABT3613 is characterized for operation from 0°C to 70°C.
For more information on this device family, see the following application reports:
D
FIFO Mailbox-Bypass Registers: Using Bypass Registers to Initialize DMA Control
(literature number SCAA007)
D
Advanced Bus-Matching/Byte-Swapping Features for Internetworking FIFO Applications
(literature number SCAA014)
D
Parity-Generate and Parity-Check Features for High-Bandwidth-Computing FIFO Applications
(literature number SCAA015)
D
Internetworking the SN74ABT3614
(literature number SCAA018)
D
Metastability Performance of Clocked FIFOs
(literature number SCZA004)
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Copyright 1998, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
SN74ABT3613
64 × 36 CLOCKED FIRST-IN, FIRST-OUT MEMORY
WITH BUS MATCHING AND BYTE SWAPPING
SCBS128F – JULY 1992 – REVISED APRIL 1998
2
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
93
94
95
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120
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91
92
60
A24
A25
A26
A27
A28
GND
A30
A31
A32
A34
A35
GND
B35
B34
B33
B32
B31
B30
GND
B29
B28
B27
B26
B25
B24
B23
AF
FF
CSA
CLKA
W/RA
PEFA
MBF2
MBA
FS1
FS0
ODD/EVEN
RST
GND
SW1
SW0
SIZ0
MBF1
PEFB
PGB
W/RB
CLKB
ENB
CSB
CC
V
CC
V
CC
V
BE
PCB PACKAGE
(TOP VIEW)
A33
CC
V
NC
SIZ1
PGA
B22
B21
GND
B20
B19
B18
B17
B16
B15
B14
B13
B12
B1 1
B10
GND
B9
B8
B7
V
CC
B6
B5
B4
B3
GND
B2
B1
B0
EF
AE
NC
A23
A22
A21
GND
A20
A19
A18
A17
A16
A15
A14
A13
A12
A1 1
A10
GND
A9
A8
A7
V
CC
A6
A5
A4
A3
GND
A2
A1
A0
NC
NC
A29
ENA
NC – No internal connection
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SN74ABT3613
64 × 36 CLOCKED FIRST-IN, FIRST-OUT MEMORY
WITH BUS MATCHING AND BYTE SWAPPING
SCBS128F – JULY 1992 – REVISED APRIL 1998
3
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
GND
NC
NC
A0
A1
A2
GND
A3
A4
A5
A6
V
CC
A7
A8
A9
GND
A10
A11
V
CC
A12
A13
A14
GND
A15
A16
A17
A18
A19
A20
GND
A21
A22
A23
GND
AE
EF
B0
B1
B2
GND
B3
B4
B5
B6
V
CC
B7
B8
B9
GND
B10
B11
V
CC
B12
B13
B14
GND
B15
B16
B17
B18
B19
B20
GND
B21
B22
B23
PQ PACKAGE
†
(TOP VIEW)
AF
FFVENA
CLKA
W/RA
PGA
PEFA
GND
MBF2
MBA
FS0
ODD/EVEN
RST
GNDBESW1
SW0
SIZ1
SIZ0
MBF1
GND
PGB
W/RB
CLKB
ENB
CSBNCNC
A24
A25
A26
GND
A27
A29
A30
A31
A32
GND
A33
A34
A35
GND
B35
B34
GND
B32
B31
B30
B29
B28
B27
GND
B26
B25
B24
CC
A28
B33
CC
V
CSA
FS1
PEFB
CC
V
V
CC
CC
V
CC
V
NC – No internal connection
†
Uses Yamaichi socket IC51-1324-828
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17 1615 14 13 12 11 10 9 8 7 6 5 4 3 2 1 132 130 128 126 124 122 120 118
131 129 127 125 123 121 119 117
51 52 53 54 55 56 5758 59 60 61 62 63 64 65 66 6768 70 72 74 76 78 80 8269 71 73 75 77 79 81 83
SN74ABT3613
64 × 36 CLOCKED FIRST-IN, FIRST-OUT MEMORY
WITH BUS MATCHING AND BYTE SWAPPING
SCBS128F – JULY 1992 – REVISED APRIL 1998
4
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
functional block diagram
Port-A
Control
Logic
AF
FIFO
Programmable-Flag
Offset Register
Port-B
Control
Logic
BE
Parity
Gen/Check
Mail2
Register
Status-Flag
Logic
Write
Pointer
CLKA
CSA
W/RA
ENA
MBA
FF
FS0
A0–A35
Device
Control
64 × 36
SRAM
Output Register
Mail1
Register
Read
Pointer
FS1
MBF2
AE
CLKB
CSB
ENB
36
RST
MBF1
EF
B0–B35
PEFB
PGB
ODD/
EVEN
Input Register
W/RB
Parity
Gen/Check
PEFA
PGA
Parity
Generation
SIZ0
SIZ1
SW0
SW1
Bus Matching and
Byte Swapping
36
SN74ABT3613
64 × 36 CLOCKED FIRST-IN, FIRST-OUT MEMORY
WITH BUS MATCHING AND BYTE SWAPPING
SCBS128F – JULY 1992 – REVISED APRIL 1998
5
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
Terminal Functions
TERMINAL
NAME
I/O DESCRIPTION
A0–A35 I/O Port-A data. The 36-bit bidirectional data port for side A.
AE
O
(port B)
Almost-empty flag. Programmable almost-empty flag synchronized to CLKB. AE is low when the number of 36-bit
words in the FIFO is less than or equal to the value in offset register X.
AF
O
(port A)
Almost-full flag. Programmable almost-full flag synchronized to CLKA. AF is low when the number of 36-bit empty
locations in the FIFO is less than or equal to the value in offset register X.
B0–B35 I/O Port-B data. The 36-bit bidirectional data port for side B.
BE
I
Big-endian select. Selects the bytes on port B used during byte or word FIFO reads. A low on BE selects the
most-significant bytes on B0–B35 for use, and a high selects the least-significant bytes.
CLKA I
Port-A clock. CLKA is a continuous clock that synchronizes all data transfers through port A and can be
asynchronous or coincident to CLKB. FF
and AF are synchronized to the low-to-high transition of CLKA.
CLKB I
Port-B clock. CLKB is a continuous clock that synchronizes all data transfers through port B and can be
asynchronous or coincident to CLKA. Port-B byte swapping and data-port-sizing operations are also synchronous
to the low-to-high transition of CLKB. EF
and AE are synchronized to the low-to-high transition of CLKB.
CSA
I
Port-A chip select. CSA must be low to enable a low-to-high transition of CLKA to read or write data on port A. The
A0–A35 outputs are in the high-impedance state when CSA
is high.
CSB
I
Port-B chip select. CSB must be low to enable a low-to-high transition of CLKB to read or write data on port B. The
B0–B35 outputs are in the high-impedance state when CSB
is high.
EF
O
(port B)
Empty flag. EF is synchronized to the low-to-high transition of CLKB. When EF is low, the FIFO is empty and reads
from its memory are disabled. Data can be read from the FIFO to the output register when EF
is high. EF is forced
low when the device is reset and is set high by the second low-to-high transition of CLKB after data is loaded into
empty FIFO memory.
ENA I Port-A enable. ENA must be high to enable a low-to-high transition of CLKA to read or write data on port A.
ENB I Port-B enable. ENB must be high to enable a low-to-high transition of CLKB to read or write data on port B.
FF
O
(port A)
Full flag. FF is synchronized to the low-to-high transition of CLKA. When FF is low, the FIFO is full and writes to its
memory are disabled. FF
is forced low when the device is reset and is set high by the second low-to-high transition
of CLKA after reset.
FS1
FS0
I
Flag offset selects. The low-to-high transition of RST latches the values of FS0 and FS1, which selects one of four
preset values for the AE
flag and AF flag offset.
MBA I
Port-A mailbox select. A high level on MBA chooses a mailbox register for a port-A read or write operation. When
the A0–A35 outputs are active, mail2 register data is output.
MBF1
O
Mail1 register flag. MBF1 is set low by the low-to-high transition of CLKA that writes data to the mail1 register. W rites
to the mail1 register are inhibited while MBF1
is low. MBF1 is set high by a low-to-high transition of CLKB when a
port-B read is selected and both SIZ1 and SIZ0 are high. MBF1
is set high when the device is reset.
MBF2
O
Mail2 register flag. MBF2 is set low by the low-to-high transition of CLKB that writes data to the mail2 register. W rites
to the mail2 register are inhibited while MBF2
is low. MBF2 is set high by a low-to-high transition of CLKA when a
port-A read is selected and MBA is high. MBF2
is set high when the device is reset.
ODD/EVEN
I
Odd/even parity select. Odd parity is checked on each port when ODD/EVEN is high and even parity is checked when
ODD/EVEN
is low. ODD/EVEN also selects the type of parity generated for each port if parity generation is enabled
for a read operation.
PEFA
O
(port A)
Port-A parity error flag. When any byte applied to terminals A0–A35 fails parity, PEFA is low. Bytes are organized
as A0–A8, A9–A17, A18–A26, and A27–A35, with the most-significant bit of each byte serving as the parity bit. The
type of parity checked is determined by the state of ODD/EVEN
.
The parity trees used to check the A0–A35 inputs are shared by the mail2 register to generate parity if parity
generation is selected by PGA; therefore, if a mail2 read with parity generation is set up by having CSA low, ENA
high, W/R
A low, MBA high, and PGA high, the PEF A flag is forced high, regardless of the state of the A0–A35 inputs.
SN74ABT3613
64 × 36 CLOCKED FIRST-IN, FIRST-OUT MEMORY
WITH BUS MATCHING AND BYTE SWAPPING
SCBS128F – JULY 1992 – REVISED APRIL 1998
6
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
Terminal Functions (Continued)
TERMINAL
NAME
I/O DESCRIPTION
PEFB
O
(port B)
Port-B parity error flag. When any valid byte applied to terminals B0–B35 fails parity, PEFB is low. Bytes are
organized as B0–B8, B9–B17, B18–B26, and B27–B35 with the most-significant bit of each byte serving as the parity
bit. A byte is valid when it is used by the bus size selected for port B. The type of parity checked is determined by
the state of ODD/EVEN
.
The parity trees used to check the B0–B35 inputs are shared by the mail1 register to generate parity if parity
generation is selected by PGB; therefore, if a mail1 read with parity generation is set up by having CSB
low, ENB
high, W/R
B low, SIZ1 and SIZ0 high, and PGB high, the PEFB flag is forced high, regardless of the state of the
B0–B35 inputs.
PGA I
Port-A parity generation. Parity is generated for data reads from the mail2 register when PGA is high. The type of
parity generated is selected by the state of ODD/EVEN
. Bytes are organized as A0–A8, A9–A17, A18–A26, and
A27–A35. The generated parity bits are output in the most-significant bit of each byte.
PGB I
Port-B parity generation. Parity is generated for data reads from port B when PGB is high. The type of parity
generated is selected by the state of ODD/EVEN
. Bytes are organized as B0–B8, B9–B17, B18–B26, and B27–B35.
The generated parity bits are output in the most-significant bit of each byte.
RST
I
Reset. T o reset the device, four low-to-high transitions of CLKA and four low-to-high transitions of CLKB must occur
while RST
is low. This sets the AF, MBF1, and MBF2 flags high and the EF, AE, and FF flags low. The low-to-high
transition of RST
latches the status of the FS1 and FS0 inputs to select AF flag and AE flag offset.
SIZ0
SIZ1
I
(port B)
Port-B bus size selects. The low-to-high transition of CLKB latches the states of SIZ0, SIZ1, and BE, and the following
low-to-high transition of CLKB implements the latched states as a port-B bus size. Port-B bus sizes can be long word,
word, or byte. A high on both SIZ0 and SIZ1 accesses the mailbox registers for a port-B 36-bit write or read.
SW0
SW1
I
(port B)
Port-B byte swap selects. At the beginning of each long-word FIFO read, one of four modes of byte-order swapping
is selected by SW0 and SW1. The four modes are no swap, byte swap, word swap, and byte-word swap. Byte-order
swapping is possible with any bus-size selection.
W/RA
I
Port-A write/read select. W/RA high selects a write operation and a low selects a read operation on port A for a
low-to-high transition of CLKA. The A0–A35 outputs are in the high-impedance state when W/R
A is high.
W/RB
I
Port-B write/read select. W/RB high selects a write operation and a low selects a read operation on port B for a
low-to-high transition of CLKB. The B0–B35 outputs are in the high-impedance state when W/R
B is high.
detailed description
reset
The SN74ABT3613 is reset by taking the reset (RST
) input low for at least four port-A clock (CLKA) and four
port-B clock (CLKB) low-to-high transitions. The reset input can switch asynchronously to the clocks. A device
reset initializes the internal read and write pointers of each FIFO and forces FF
low, EF low, AE low, and the
AF
high. A reset also forces the mailbox flags (MBF1, MBF2) high. After a reset, FF is set high after two
low-to-high transitions of CLKA. The device must be reset after power up before data is written to its memory .
A low-to-high transition on the RST
input loads the AF and AE offset register (X) with the value selected by the
flag-select (FS0, FS1) inputs. The values that can be loaded into the register are shown in Table 1.
T able 1. Flag Programming
FS1 FS0 RST
AF/AE FLAG
OFFSET REGISTER (X)
H H ↑ 16
H L ↑ 12
L H ↑ 8
L L ↑ 4
SN74ABT3613
64 × 36 CLOCKED FIRST-IN, FIRST-OUT MEMORY
WITH BUS MATCHING AND BYTE SWAPPING
SCBS128F – JULY 1992 – REVISED APRIL 1998
7
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
FIFO write/read operation
The state of the port-A data (A0–A35) outputs is controlled by the port-A chip select (CSA
) and the port-A
write/read select (W/R
A). The A0–A35 outputs are in the high-impedance state when either CSA or W/RA is
high. The A0–A35 outputs are active when both CSA
and W/RA are low. Data is loaded into the FIFO from the
A0–A35 inputs on a low-to-high transition of CLKA when CSA
is low, W/RA is high, ENA is high, MBA is low,
and FFA
is high (see Table 2).
Table 2. Port-A Enable Function Table
CSA W/RA ENA MBA CLKA
A0–A35 OUTPUTS PORT FUNCTION
H X X X X In high-impedance state None
L H L X X In high-impedance state None
L H H L ↑ In high-impedance state FIFO write
L H H H ↑ In high-impedance state Mail1 write
L L L L X Active, mail2 register None
L L H L ↑ Active, mail2 register None
L L L H X Active, mail2 register None
L L H H ↑ Active, mail2 register Mail2 read (set MBF2 high)
The state of the port-B data (B0–B35) outputs is controlled by the port-B chip select (CSB) and the port-B
write/read select (W/R
B). The B0–B35 outputs are in the high-impedance state when either CSB or W/RB is
high. The B0–B35 outputs are active when both CSB
and W/RB are low. Data is read from the FIFO to the
B0–B35 outputs by a low-to-high transition of CLKB when CSB
is low, W/RB is low, ENB is high, EFB is high,
and either SIZ0 or SIZ1 is low (see Table 3).
Table 3. Port-B Enable Function Table
CSB W/RB ENB SIZ1, SIZ0 CLKB
B0–B35 OUTPUTS PORT FUNCTION
H X X X X In high-impedance state None
L H L X X In high-impedance state None
L H H One, both low ↑ In high-impedance state None
L H H Both high ↑ In high-impedance state Mail2 write
L L L One, both low X Active, FIFO output register None
L L H One, both low ↑ Active, FIFO output register FIFO read
L L L Both high X Active, mail1 register None
L L H Both high ↑ Active, mail1 register Mail1 read (set MBF1 high)
The setup- and hold-time constraints to the port clocks for the port-chip selects (CSA, CSB) and write/read
selects (W/R
A, W/RB) are only for enabling write and read operations and are not related to high-impedance
control of the data outputs. If a port enable is low during a clock cycle, the port chip select and write/read select
can change states during the setup- and hold-time window of the cycle.
SN74ABT3613
64 × 36 CLOCKED FIRST-IN, FIRST-OUT MEMORY
WITH BUS MATCHING AND BYTE SWAPPING
SCBS128F – JULY 1992 – REVISED APRIL 1998
8
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
synchronized FIFO flags
Each FIFO flag is synchronized to its port clock through two flip-flop stages. This is done to improve flag reliability
by reducing the probability of metastable events on the output when CLKA and CLKB operate asynchronously
to one another. FF
and AF are synchronized to CLKA. EF and AE are synchronized to CLKB. Table 4 shows
the relationship of each port flag to the level of FIFO fill.
Table 4. FIFO Flag Operation
NUMBER OF 36-BIT
SYNCHRONIZED
TO CLKB
SYNCHRONIZED
TO CLKA
WORDS IN THE FIFO
†
EF AE AF FF
0 L L H H
1 to X H L H H
(X + 1) to [64 – (X + 1)] H H H H
(64 – X) to 63 H H L H
64 H H L L
†
X is the value in the AE flag and AF flag offset register.
empty flag (EF)
The FIFO EF is synchronized to the port clock that reads data from its array (CLKB). When the empty flag is
high, new data can be read to the FIFO output register. When the empty flag is low, the FIFO is empty and
attempted FIFO reads are ignored. When reading the FIFO with a byte or word size on port B, EF
is set low when
the fourth byte or second word of the last long word is read.
The FIFO read pointer is incremented each time a new word is clocked to the output register. A word written
to the FIFO can be read to the FIFO output register in a minimum of three port-B clock (CLKB) cycles. An EF
is low if a word in memory is the next data to be sent to the FIFO output register and two cycles of the port clock
that reads data from the FIFO have not elapsed since the time the word was written. The FIFO EF
is set high
by the second low-to-high transition of CLKB and the new data word can be read to the FIFO output register
in the following cycle.
A low-to-high transition on CLKB begins the first synchronization cycle of a write if the clock transition occurs
at time t
sk1
, or greater, after the write. Otherwise, the subsequent clock cycle can be the first synchronization
cycle (see Figure 9).
full flag (FF)
The FIFO FF is synchronized to the port clock that writes data to its array (CLKA). When FF is high, a memory
location is free in the SRAM to receive new data. No memory locations are free when FF
is low and attempted
writes to the FIFO are ignored.
Each time a word is written to the FIFO, the write pointer is incremented. From the time a word is read from the
FIFO, the previous memory location is ready to be written in a minimum of three CLKA cycles. FF
is low if fewer
than two CLKA cycles have elapsed since the next memory-write location has been read. The second
low-to-high transition on the FF
synchronizing clock after the read sets the FF high and data can be written in
the following clock cycle.
A low-to-high transition on CLKA begins the first synchronization cycle of a read if the clock transition occurs
at time t
sk1
, or greater, after the read. Otherwise, the subsequent clock cycle can be the first synchronization
cycle (see Figure 10).
SN74ABT3613
64 × 36 CLOCKED FIRST-IN, FIRST-OUT MEMORY
WITH BUS MATCHING AND BYTE SWAPPING
SCBS128F – JULY 1992 – REVISED APRIL 1998
9
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
almost-empty flag (AE)
The FIFO AE flag is synchronized to the port clock that reads data from its array (CLKB). The almost-empty state
is defined by the value of the AF
and AE offset register (X). This register is loaded with one of four preset values
during a device reset (see
reset
). An AE flag is low when the FIFO contains X or fewer long words in memory
and is high when the FIFO contains (X + 1) or more long words.
Two low-to-high transitions of CLKB are required after a FIFO write for the AE
flag to reflect the new level of
fill; therefore, the AE
flag of a FIFO containing (X + 1) or more long words remains low if two CLKB cycles have
not elapsed since the write that filled the memory to the (X + 1) level. An AE
flag is set high by the second
low-to-high transition of CLKB after the FIFO write that fills memory to the (X + 1) level. A low-to-high transition
of CLKB begins the first synchronization cycle if it occurs at time t
sk2
, or greater, after the write that fills the FIFO
to (X + 1) long words. Otherwise, the subsequent CLKB cycle can be the first synchronization cycle
(see Figure 11).
almost-full flag (AF)
The FIFO AF flag is synchronized to the port clock that writes data to its array (CLKA). The almost-full state is
defined by the value of the AF
and AE offset register (X). This register is loaded with one of four preset values
during a device reset (see
reset
). An AF flag is low when the FIFO contains (64 – X) or more long words in
memory and is high when the FIFO contains [64 – (X + 1)] or less long words.
Two low-to-high transitions of CLKA are required after a FIFO read for the AF
flag to reflect the new level of fill;
therefore, the AF
flag of a FIFO containing [64 – (X + 1)] or fewer words remains low if two CLKA cycles have
not elapsed since the read that reduced the number of long words in memory to [64 – (X + 1)]. An AF
flag is
set high by the second low-to-high transition of CLKA after the FIFO read that reduces the number of long words
in memory to [64 – (X + 1)]. A low-to-high transition of CLKA begins the first synchronization cycle if it occurs
at time t
sk2
, or greater, after the read that reduces the number of long words in memory to [64 – (X + 1)].
Otherwise, the subsequent CLKA cycle can be the first synchronization cycle (see Figure 12).
mailbox registers
Two 36-bit bypass registers (mail1, mail2) are on board the SN74ABT3613 to pass command and control
information between port A and port B without putting it in queue. A low-to-high transition on CLKA writes
A0–A35 data to the mail1 register when a port-A write is selected by CSA
, W/RA, and ENA, and MBA is high.
A low-to-high transition on CLKB writes B0–B35 data to the mail2 register when a port-B write is selected by
(CSB
, W/RB, and ENB) and both SIZ0 and SIZ1 are high. Writing data to a mail register sets the corresponding
flag (MBF1
or MBF2) low. Attempted writes to a mail register are ignored while the mail flag is low.
When the port-B data outputs (B0–B35) are active, the data on the bus comes from the FIFO output register
when either one or both SIZ1 and SIZ0 are low and from the mail1 register when both SIZ1 and SIZ0 are high.
The mail1 register flag (MBF1
) is set high by a rising CLKB edge when a port-B read is selected by CSB, W/RB,
and ENB, and both SIZ1 and SIZ0 are high. The mail2 register flag (MBF2
) is set high by a rising CLKA edge
when a port-A read is selected by CSA
, W/RA, and ENA and MBA is high. The data in the mail register remains
intact after it is read and changes only when new data is written to the register.
SN74ABT3613
64 × 36 CLOCKED FIRST-IN, FIRST-OUT MEMORY
WITH BUS MATCHING AND BYTE SWAPPING
SCBS128F – JULY 1992 – REVISED APRIL 1998
10
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
dynamic bus sizing
The port-B bus can be configured in a 36-bit long word, 18-bit word, or 9-bit byte format for data read from the
FIFO. Word- and byte-size bus selections can utilize the most-significant bytes of the bus (big endian) or
least-significant bytes of the bus (little endian). Port-B bus size can be changed dynamically and synchronous
to CLKB to communicate with peripherals of various bus widths.
The levels applied to the port-B bus-size select (SIZ0, SIZ1) inputs and the big-endian select (BE
) input are
stored on each CLKB low-to-high transition. The stored port-B bus-size selection is implemented by the next
rising edge on CLKB according to Figure 1.
Only 36-bit long-word data is written to or read from the FIFO memory on the SN74ABT3613. Bus-matching
operations are done after data is read from the FIFO RAM. Port-B bus sizing does not apply to mail-register
operations.
Read From FIFO
Write to FIFO
(a) LONG-WORD SIZE
1st: Read From FIFO
2nd: Read From FIFO
(b) WORD SIZE – BIG ENDIAN
BYTE ORDER ON PORT A:
A35 A27 A26 A18 A17 A9 A8 A0
B35 B27 B26 B18 B17 B9 B8 B0
XLL
BE
SIZ1 SIZ0
ABCD
ABCD
AB
CD
B35 B27 B26 B18 B17 B9 B8 B0
B35 B27 B26 B18 B17 B9 B8 B0
LLH
BE
SIZ1 SIZ0
1st: Read From FIFO
2nd: Read From FIFO
(c) WORD SIZE – LITTLE ENDIAN
CD
AB
B35 B27 B26 B18 B17 B9 B8 B0
B35 B27 B26 B18 B17 B9 B8 B0
HLH
BE
SIZ1 SIZ0
Figure 1. Dynamic Bus Sizing
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