Aeroflex Circuit Technology

5

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

Loop Test

Upon receipt from the subsystem, the last word

to be transmitted within a given message

transfer (command 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-BC,

Short Loop verification. A LOOPERR (.5us typ)

low pulse indicates a mismatch between the

stored and looped word.

The CT2565 also

initiates a handshake with a memory write to the

subsystem

for

user-defined,

"long

loop"

(subsystem, CT2565, subsystem) verification.

Note that both short and long loop testing are

initiated for all transfers (on the last word

transmitted to 1553). Subsystems response to

use Long Loop Test is to compare the loaded

word to what was looped back into memory.

RECEIVE

TRANSMIT

Control Word

Control Word

Receive Command

Transmit Command

Data 1

Looped Command Word

•

RTU Status

•

Data 1

Last Data

•

Looped Data Word

•

RTU Status

Last Data

Table 3 – BC Memory Allocation

15

8

0

NOT USED

BUS CHANNEL A/

B

NOT USED

MASK BROADCAST BIT

NOT USED

MODE CODE

BROADCAST

RT-RT

BIT

DEFINITION

BUS CHANNEL A/B

When logic "1" transmits over 1553 Bus A.

When logic "0" transmits over 1553 Bus B

(See note)

MASK BROADCAST BIT

Always set to "0"

MODE CODE

Command Word count field signifies mode code type

BROADCAST

Multiple RTU’s addressed, no status word expected

RT-RT

When set, RTU(b) transmits, RTU(a) receives. Both RTU Status Words

are validated and sent to subsystem.

Note: Messages-transmission (routing) status pin (pin 16, Chan A/B) becomes active after loading the control word and command word

respectively. The signal is cleared by RESET or EOM low.

Figure 4 – BC Control Word