Aeroflex Circuit Technology

14

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

TRANSFER/CONDITION

DESCRIPTION

ERROR SIGNAL

PIN

COMMAND WORD

Invalid Word Format

Invalid Command (format error)

Sync, bit count invalid.

Operation disagreement (e.g. Broadcast and

Transmit bits set)

None; input ignored

MSGERR (also; SW bit)

-

30

Handshake Failure

BUSREQ to BUSGRNT timeout

HSFAIL, suppress

SOM, continue

5

78

Illegal Mode Command

Subsystem set ILLCMD (pin 48).

SW message error bit set

RT-RT Transfer

Response Timeout

Address mismatch

(Transmit) Command to Status Word time.

Transmit Command Address

address.

TIMEOUT (transmitting RT)

(also; MSGERR bit)

MSGERR (Receiving RT)

(also; MSGERR bit)

4

30

DATA WORD

Handshake Failure

Transmit Command

Receive Command

BUSREQ to BUSGRNT timeout

(Continue)

(Message terminated)

Low data word-count received.

High data word count

Continue message transfer

INCMD high, EOM

MSGERR after validation

(no transfer) SW and BIT-

Word also set.

5

9,57

30

30

LOOP WORD

Short Loop

Long Loop

Looped back through receiver.

Received word

(BC only)

LOOPER (also sets Ter-

Flag bit).

46

Notes:

(1) The HSFAIL low output is reset (high) at the start of the next message transfer (NBGRNT low).

(2) The subsystem can use the status input pins (SW) to report incorrect word count type errors.

(3) MSGERR set 7.5µS after last mid parity bit of last data word.

Table 6 – RTU Error Handling

RTU Commands

A command word transfer will be initiated by the

CT2565 after the rising edge of NBGRNT (See

Figure 14). In order to allow the command word to be

stored in user-defined memory space (separate from

data), no memory write operation (CS, WR, ADRINC

outputs) will be initiated following the usual DMA-type

handshake; a Start Of Message (pin 78: SOM low)

pulse indicates that the CMD word is currently valid on

the data bus. Note that commands are named from

the BC point-of-view (i.e., a TRANSMIT CMD dictates

that the addressed RTU must transmit data).

Transmit CMD (RT-BC)

If the subsystem is available (pin 47: SSBUSY high):

following transmission of the status word, the CT2565

will initiate a handshake/memory-read respectively for

the total number of (data) words defined by the

Command Word-word count field.

Figure 15 shows

the RTU Read/Write Timing. Note that possible data

word transfer and short-loop test errors will be

reflected in the following status word/bit word. A low

on the SSBUSY input will set the corresponding status

word flag, and no data transfer will be requested

(BUSREQ low) following transmission of the status

word.

Receive CMD (BC-RT). A DMA handshake will be

initiated for each word received over the 1553 data bus

(See Figure 16).

If successful, the respective

handshake will be followed by a corresponding

memory write.

Transfer errors such as handshake

timeout or SS BUSY will not terminate transfer

attempts for the remaining data words, error flagging

or status word transmission.

RTU(b)-RTU(a)

(Transmit/Receive).

An

RT-RT

transfer will appear to both RTU subsystems as a

standard transmit or receive command except:

(1)

transmission of the data block will not be continuous

with that of the receive CMD, and, (2) upon detection

of a command-sync field following the receive CMD,

RTU(a) will recognize an RT-RT transfer and store the

transmit CMD-address field for comparison with the

address field of the following (RTU(b) status) word

(See Figures 17 and 18). If a mismatch is detected,

RTU(a) will issue a message error. The transmitting

RTU will respond as in an RT-BC Transmit CMD.

RTU Status/Error Handling

Message transfer errors are indicated using the

TIMEOUT,

HSFAIL,

MSGERR

and

LOOPERR

RTU-status outputs (pins 4, 5, 30 and 46 respectively).

Additional

error

detection

mechanisms

available

include

status

input

manipulation

(below)

and

evaluation of the status and BIT words (See BIT

Word).

Table 6 describes error handling mechanisms related

to each stage in a message transfer (reading left to

right) as well as noting errors associated with a

specific CT2565 status output (reading right to left).

Short Loop Test. The last word to be transmitted in a

given message transfer (Status word, BIT word or

Data word) is stored in a CT2565 internal register. As

this word is transmitted to the 1553 bus, it is "looped

back"

through

the

active

receiver

channel

for

auto-RTU, "SHORTLOOP" verification. A LOOPERR

low pulse indicates a mismatch between the stored

and looped words.

Note that short loop testing is

initiated for all RTU transfers except a Broadcast

transfer.