5

COMMERCIAL TEMPERATURERANGE

256 x 36 x 2, 512 x 36 x 2, 1,024 x 36 x 2

Symbol

Name

I/O

Description

MBA

Port A Mailbox

I

A HIGH level on MBA chooses a mailbox register for a port A read or write operation. When the

Select

A0-A35 outputs are active, a HIGH level on MBA selects data from the mail2 register for output and a

LOWlevelselectsFIFO2outputregisterdataforoutput.

MBB

Port B Mailbox

I

A HIGH level on MBB chooses a mailbox register for a port B read or write operation. When the

Select

B0-B35 outputs are active, a HIGH level on MBB selects data from the mail1 register or output and a

LOWlevelselectsFIFO1outputregisterdataforoutput.

MBF1

Mail1Register

O

MBF1 is set LOW by a LOW-to-HIGH transition of CLKA that writes data to the mail1 register.

Flag

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

isreset.

MBF2

Mail2Register

O

MBF2 is set LOW by a LOW-to-HIGH transition of CLKB that writes data to the mail2 register. Writes

Flag

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 also set HIGH when

FIFO2 is reset.

RST1

FIFO1Reset

I

ToresetFIFO1,fourLOW-to-HIGHtransitionsofCLKAandfourLOW-to-HIGHtransitionsofCLKBmust

occur while RST1 is LOW. The LOW-to-HIGH transition of RST1 latches the status of FS0 and FS1 for

AFA and AEB offset selection. FIFO1 must be reset upon power up before data is written to its RAM.

RST2

FIFO2Reset

I

ToresetFIFO2,fourLOW-to-HIGHtransitionsofCLKAandfourLOW-to-HIGHtransitionsofCLKBmust

occur while RST2 is LOW. The LOW-to-HIGH transition of RST2 latches the status of FS0 and FS1 for

AFB and AEA offset selection. FIFO2 must be reset upon power up before data is written to its RAM.

W/RA

PortAWrite/

I

A HIGH selects a write operation and a LOW selects a read operation on port A for a LOW-to-HIGH

ReadSelect

transition of CLKA. The A0-A35 outputs are in the HIGH impedance state when W/RA is HIGH.

W/RB

PortBWrite/

I

A LOW selects a write operation and a HIGH selects a read operation on port B for a LOW-to-HIGH

ReadSelect

transition of CLKB. The B0-B35 outputs are in the HIGH impedance state when W/RB is LOW.

PIN DESCRIPTIONS (CONTINUED)