Aeroflex Circuit Technology

7

SCDCT2565 REV B 8/10/99 Plainview NY (516) 694-6700

RTU Response

The

addressed

RTU(s)

must

respond

(to

non-broadcast commands) within a timeout

period as shown in Figures 7, 8, and 9. Figures

10 and 11 illustrate the BC Mode Code Timing.

Status and data words received from the 1553

port are transferred to the subsystem via a

handshake and memory write operation for each

(See Message Length Checking).

BC Status/Error Handling

Message transfer errors are indicated using the

TIMEOUT, MSGERR, LOOPERR and STATERR

BC status outputs (pins 4, 30, 46 and 68

respectively).

Additional

error

detection

methods include user evaluation of status, data

and (long) loop words and/or use of the 1553B

dual redundant mode codes. Note that certain

error conditions not reflected in the current

Status Word (SW) can occur; Broadcast CMD

RT-status and post RT status response may be

accessed via the Transmit Status Word mode

command.

Transmit Bit Word. Additional status informa

tion is generated by an RTU (CT2565 for each

transfer in the form of a BIT word). This word

may

be

accessed

by

the

BC

using

the

TRANSMIT B-I-T WORD mode command. See

RTU Error Handling and Mode Code sections).

Message Length Checking. The BC stores the

command word, word-count field in an internal

register. By decrementing this register following

each data word transfer (See BC Memory

Read/Write Timing), the BC can detect an

incorrect message length.

For a description of the possible BC error,

indicators

occurring

during

each

stage

of

message transfer read from left to right in

Table 4. For a description of the possible causes

of errors within a transfer, read from right to left.

TRANSFER/CONDITION

DESCRIPTION

ERROR SIGNAL

PIN

CONTROL/COMMAND WORD 1

Handshake Failure

Memory read by BC subsystem.

No response to Bus Request within timeout

period.

BC waits for Grant

(no 1553 timing error)

-

LOOPED WORD

Short Loop Failure

Long Loop Failure

Looped back through receiver.

Received Word

DMA/Write looped word to subsystem.

LOOPERR

User Defined

46

-

RT-RT

Status-RT1, data, status-RT2 response

to follow receive, transmit, commands.

(See definitions in

STATUS/DATA WORD

below)

-

STATUS WORD

No Status Received within 15.5µS

NODT timeout

TIMEOUT

EOM

4

57

RT Address Mismatch

Command RTU Address

RTU Address

STATERR

68

Error Flag(s) Set

Status Word Response from RT:

Error Condition

STATERR

68

Broadcast Received bit Set

Response to Transmit Status Word mode

command may allow this, all others ERROR.

Broadcast Mask not set

(See BC Control Word)

STATERR

68

DATA WORD

Handshake Failure

Transmit Command

Receive Command

No subsystem response to Bus Request.

Data lost: Word Count fails.

1553 transmission gap.

BC waits for Grant.

MSGERR

Status Word response:

STATERR

30

68

Data Received from RTU

Less than word count

Greater than word count

Transmit Command (RTU response)

More data received than requested.

MSGERR and EOM

MSGERR and EOM

4

30

Data after Status Set

(all extra words)

Transmit Command: data words received

after status to subsystem.

DMA/memory write

(for each)

-

FORMAT ERROR

-

MSGERR

30

Notes:

(1) LOOPERR is a .5µS pulse which occurs near DMA handshake for loop back word.

(2) TIMEOUT is a 40/160nS pulse which occurs 19.5µS ±0.5µS after the mid-bit parity of the last word onto the bus.

(3) STATERR is a 120/166nS pulse which occurs during the status word DMA handshake.

(4) MSGRR is a 40/160nS pulse which occurs approximately 100nS before INCMD goes high. It is triggered by NODT going inactive (i.e.,

low word count).

Table 4 – BC Error Handling