SN74ACT3638

512

× 32 × 2

CLOCKED BIDIRECTIONAL FIRST-IN, FIRST-OUT MEMORY

SCAS228D – JUNE 1992 – REVISED APRIL 1998

5

POST OFFICE BOX 655303

Terminal Functions

TERMINAL

NAME

I/O

DESCRIPTION

A0 – A31

I/O

Port-A data. The 32-bit bidirectional data port for side A.

AEA

O

(port A)

Port-A almost-empty flag. Programmable flag synchronized to CLKA. AEA is low when the number of words in FIFO2

is less than or equal to the value in the almost-empty A offset register, X2.

AEB

O

(port B)

Port-B almost-empty flag. Programmable flag synchronized to CLKB. AEB is low when the number of words in FIFO1

is less than or equal to the value in the almost-empty B offset register, X1.

AFA

O

(port A)

Port-A almost-full flag. Programmable flag synchronized to CLKA. AFA is low when the number of empty locations in

FIFO1 is less than or equal to the value in the almost-full A offset register, Y1.

AFB

O

(port B)

Port-B almost-full flag. Programmable flag synchronized to CLKB. AFB is low when the number of empty locations

in FIFO2 is less than or equal to the value in the almost full B offset register, Y2.

B0 – B31

I/O

Port-B data. The 32-bit bidirectional data port for side B.

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. IRA, ORA, AFA, and AEA are synchronous 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. IRB, ORB, AFB, and AEB are synchronous 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 – A31 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 – B31 outputs are in the high-impedance state when CSB is high.

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.

FS1, FS0

I

Flag-offset selects. The low-to-high transition of a FIFO reset input latches the values of FS0 and FS1. If either FS0

or FS1 is high when a reset input goes high, one of three preset values is selected as the offset for the FIFO almost-full

and almost-empty flags. If both FIFOs are reset simultaneously and both FS0 and FS1 are low when RST1 and RST2

go high, the first four writes to FIFO1 program the almost-full and almost-empty offsets for both FIFOs.

IRA

O

(port A)

Port-A input-ready flag. IRA is synchronized to the low-to-high transition of CLKA. When IRA is low, FIFO1 is full and

writes to its array are disabled. When FIFO1 is in retransmit mode, IRA indicates when the memory has been filled

to the point of the retransmit data and prevents further writes. IRA is set low when FIFO1 is reset and is set high on

the second low-to-high transition of CLKA after reset.

IRB

O

(port B)

Port-B input-ready flag. IRB is synchronized to the low-to-high transition of CLKB. When IRB is low, FIFO2 is full and

writes to its array are disabled. IRB is set low when FIFO2 is reset and is set high on the second low-to-high transition

of CLKB after reset.

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 – A31 outputs are active, a high level on MBA selects data from the mail2 register for output and a low level selects

FIFO2 output-register data for output.

MBB

I

Port-B mailbox select. A high level on MBB chooses a mailbox register for a port-B read or write operation. When the

B0 – B31 outputs are active, a high level on MBB selects data from the mail1 register for output and a low level selects

FIFO1 output-register data for 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. Writes

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 MBB is high. MBF1 is set high when FIFO1 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. Writes

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 FIFO2 is reset.

ORA

O

(port A)

Port-A output-ready flag. ORA is synchronized to the low-to-high transition of CLKA. When ORA is low, FIFO2 is empty

and reads from its memory are disabled. Ready data is present on the output register of FIFO2 when ORA is high.

ORA is forced low when FIFO2 is reset and goes high on the third low-to-high transition of CLKA after a word is loaded

to empty memory.