Pin Names

Description

A Bus Data InputsData Outputs

B Bus Data InputsData Outputs

APAR BPAR

A and B Bus Parity Inputs

ODDEVEN

ODDEVEN Parity Select Active

LOW for EVEN Parity

GBA GAB

Output Enables for A or B Bus

Active LOW

SEL

Select Pin for Feed-Through or

Generate Mode LOW for Generate

Mode

LEA LEB

Latch Enables for A and B Latches

HIGH for Transparent Mode

ERRA ERRB

Error Signals for Checking

Generated Parity with Parity In

LOW if Error Occurs

Functional Description

The ’AC’ACT899 has three principal modes of operation

which are outlined below These modes apply to both the A-

to-B and B-to-A directions

Bus A (B) communicates to Bus B (A) parity is generat-

ed and passed on to the B (A) Bus as BPAR (APAR) If

LEB (LEA) is HIGH and the Mode Select (SEL) is LOW

the parity generated from B 07

(A 07 ) can be

checked and monitored by ERRB (ERRA)

Bus A (B) communicates to Bus B (A) in a feed-through

mode if SEL is HIGH Parity is still generated and

checked as ERRA and ERRB in the feed-through mode

(can be used as an interrupt to signal a dataparity bit

error to the CPU)

Independent Latch Enables (LEA and LEB) allow other

permutations of generatingchecking (see Function Ta-

ble below)

Function Table

Inputs

Operation

GAB

GBA

SEL

LEA

LEB

H

H

X

X

X

Busses A and B are TRI-STATE

H

L

L

L

H

Generates parity from B 07 based on OE (Note 1) Generated parity

ERRB

H

L

L

H

H

Generates parity from B 07 based on OE Generated parity

x

APAR Generated parity checked against BPAR and output as ERRB

Generated parity also fed back through the A latch for generatecheck

as ERRA

H

L

L

X

L

Generates parity from B latch data based on OE Generated parity

output as ERRB

H

L

H

X

H

BPARB 07

checked against BPAR and output as ERRB

H

L

H

H

H

BPARB 07

Feed-through mode Generated parity checked against BPAR and

output as ERRB Generated parity also fed back through the A latch for

generatecheck as ERRA

L

H

L

H

L

Generates parity for A 07 based on OE Generated parity

x

BPAR Generated parity checked against APAR and output as ERRA

L

H

L

H

H

Generates parity from A 07 based on OE Generated parity

x

BPAR Generated parity checked against APAR and output as ERRA

Generated parity also fed back through the B latch for generatecheck

as ERRB

L

H

L

L

X

Generates parity from A latch data based on OE Generated parity

output as ERRA

L

H

H

H

L

APARA 07

Feed-through mode Generated parity checked against APAR and

output as ERRA

L

H

H

H

H

APARA 07

Feed-through mode Generated parity checked against APAR and

output as ERRA Generated parity also fed back through the B latch for

generatecheck as ERRB

Note 1

2