11.7

9

IDT49C465/A

32-BIT FLOW-THRU ERROR DETECTION AND CORRECTION UNIT

MILITARY AND COMMERCIAL TEMPERATURE RANGES

DIAGNOSTIC DATA FORMAT (SYSTEM BUS)

DIAGNOSTIC FEATURES — DETAILED DESCRIPTION

Mode 2-0

x11

“NORMAL” Mode

In this mode, operation is “Normal” or non-diagnostic.

x10

“GENERATE-DETECT” Mode

When the EDC unit is in the “Generate-Detect” Mode, data is not corrected or altered by the error correction network.

(Also referred to as the “Detect-only” Mode.)

000

“ERROR-DATA-OUTPUT” Mode

In this mode, the 32-bit data from the Error-Data Register is output on the SD bus.

Error Data Register: The uncorrected data from the Memory Data bus input latch is stored in the Error-Data Register

if the error counter contents indicates “0” and there is a positive transition on the SYNCLK input when the

ERR signal is

low. Thus, the Error-Data Register contains memory data corresponding to the first error to occur since the register was

cleared. This register is cleared by pulling the

CLEAR input low. The register is read via the System Data bus by entering

the “Error-Data-Output” Mode and enabling the System Data bus output drivers.

All-Zero-Data: The Error-Data Register can be used as an “all-zero-data” data source for memory initialization in systems

where the initialization process is to be done entirely by hardware.

x01

“DIAGNOSTIC-OUTPUT” Mode

In this mode, data from the diagnostic registers, the PCBI bus and the CBI bus is output on the SD bus.

Direct Checkbit Readback: Internal data paths allow both the “Partial-CheckBit-Input” bus and the data in the “CheckBit-

Input” latch to be read directly by the system bus for diagnostic purposes. Both the Checkbit Input Bus and the Partial

Checkbit Input Bus are read via the System Data bus by entering the “Diagnostic-Output” Mode and enabling the System

Data bus output drivers. The checkbits are output on System Data bus bits 0-7; the Partial Checkbits are output on bits

8-15.

Syndrome Register: After an error has been detected, the syndrome bits generated are clocked into the internal

Syndrome Register if the error counter contents indicates “0” and there is a positive transition on the SYNCLK input when

the

ERR signal is low. This register is cleared by pulling the CLEAR input low. The register is read via the System Data

bus by entering the “Diagnostic-Output” Mode and enabling the System Data bus outputs. This data is output on SD

bits 16-23.

Error Counter: The 4-bit on-board error counter is incremented if the error counter contents do not indicate FF HEX, which

corresponds to a count of 15, and there is a positive transition on the SYNCLK input when the

ERR signal is low. This

counter is cleared by pulling the

CLEAR input low. The counter is read via the System Data bus by entering the

“Diagnostic-Output” Mode and enabling the System Data bus output drivers. This data is output on System Data bus

bits 24-27.

Test Register: These 2 bits are reserved for factory diagnostics only and must not be used by system software. This data

is output on System Data bus bits 28-29.

Error-Type Register: The Error-Type Register, clocked by the SYNCLK input, saves 2 bits which indicate whether a

recorded error was a single or a multiple-bit error. This register holds only the first error type to occur after the last Clear

operation. This data is output on System Data bus bits 30-31.

100

Direct Read-Path Checkbit Injection: In the “Checkbit-Injection” Mode, bits 0-7 of the System Data input latch are

presented to the inputs of the Checkbit Input latch. If MLE is strobed, the checkbit latch will be loaded with this value in

place of the checkbits from memory. By inserting various checkbit values, operation of the correction function of the EDC

can be verified “on-board”. Except for the “Checkbit-Injection” function, operation in this mode is identical to “Normal” Mode

operation.

2552 tbl 03

Byte 3

Byte 2

Byte 1

Byte 0

Checkbits

0

8 7

16 15

24 23

31

Partial Checkbits

76

5

4

3

2

1

0

S

M

-

-

2

2

2

2

Syndrome bits

27

Error

Counter

Error

Type

Re-

served

Latched Data

Data Out (Unlatched)

7

6

5

4

3

210

7

6

5

4

3

2

1

0

2552 drw 12

30

3

0

1

2