HI-1575

FIGURE 2. STATUS AND MODE REGISTER

Bit Name

0

TXDISA

R/W

0

Writing TXDISA to a '1' disables the transmitter for MIL-STD-1553 bus A

1

TXDISB

R/W

0

Writing TXDISB to a '1' disables the transmitter for MIL-STD-1553 bus B

2

RENA

R/W

1

Setting RENA to a '1' enables the receiver for MIL-STD-1553 bus A. A '0' disables the

receiver causing the HI-1575 to ignore all activity on bus A.

3

RENB

R/W

1

Setting RENB to a '1' enables the receiver for MIL-STD-1553 bus B. A '0' disables the

receiver causing the HI-1575 to ignore all activity on bus B.

4

TXSYNC

R/W

0

The TXSYNC bit is logically ORed with the SYNC input pin during host write cycles to the

Transmit Data Register (TX). If TXSYNC OR SYNC is a '1' the transmitter prefixes the

transmitted word with a MIL-STD-1553 Command Sync. If TXSYNC OR SYNC is a '0'

during a write to TX, then the transmitted word has a MIL-STD-1553 Data Sync.

5

CHAN

R/W

0

The CHAN bit is logically ORed with the

/CHB input pin and the result used to Select

between MIL-STD-1553 bus A or B during write transfers to the TX register, or reading data

from the RX registers. When CHAN OR

/CHB is a '0' during a transmit operation,

data is transmitted on MIL-STD-1553 bus A. When the result is a '1', MIL-STD-1553

bus B is selected. During HI-1575 data read cycles, if CHAN OR

/CHB is a '0', the RXA

register is accessed, and if CHAN OR

/CHB is a '1' then the data is read from RXB.

6

-

Read-only

0

Not used. Internally set to '0'.

7

RCVA

Read-only

0

This bit reflects the state of the RCVA output pin. RCVA goes high whenever a new word is

received on MIL-STD-1553 bus A. The received word may be read by the host from the RXA

register. RCVA is reset on reading RXA or if the HI-1575 detects a new word arriving on bus A.

If the data words are contiguous, then RCVA will be high for about 3 us before the new word

resets it. The data is still available in the RXA register and may be retreived any time up until

the RCVA flag goes high again. If the user does not read the data, the word is lost when

the RCVA flag goes high on reception of the next word.

8

RSYNCA

Read-only

0

RSYNCA indicates the Sync of the last MIL-STD-1553 word received on bus A. RSYNCA is a

'0' for a Data sync, and a '1' for a Command Sync. When the RXA register is read, the

RSYNCA value is also output on the SYNC I/O pin.

9

GAPA

Read-only

0

GAPA is a '1' when there is no activity detected on MIL-STD-1553 bus A, for example during an

inter-message gap. GAPA is a '0' whenever the HI-1575 detects bus traffic.

10

ERRORA

Read-only

0

ERRORA goes high when the HI-1575 Manchester decoder receives an incorrectly encoded

word on MIL-STD-1553 bus A

11

RCVB

Read-only

0

Same function as RCVA but for MIL-STD-1553 bus B.

12

RSYNCB

Read-only

0

Same function as RSYNCA but for MIL-STD-1553 bus B.

13

GAPB

Read-only

0

Same function as GAPA but for MIL-STD-1553 bus B.

14

ERRORB

Read-only

0

Same function as ERRORA but for MIL-STD-1553 bus B.

15

SENDDATA Read-only

1

SENDDATA goes high approximately 3.5 us after the start of a MIL-STD-1553 word

transmission. SENDATA goes low approximately 18.5 us after the start of a MIL-STD-1553

word transmission. If new a new data word is written to the TX register while SENDDATA is

high, that word will be transmitted contiguously after the currently transmitting word.

R/W

Default

Description

CHA

CHA

CHA

CHA

15 14 13 12 11 10

9876543210

MSB

LSB

HOLT INTEGRATED CIRCUITS

4

0

STATUS & MODE REGISTER (SAM)