Datasheet

DS21Q50

50 of 87

14. ADDITIONAL (Sa) AND INTERNATIONAL (Si) BIT OPERATION

On the receiver, the RAF and RNAF registers always report the data as it is received in the additional (Sa)

and international (Si) bit locations. The RAF and RNAF registers are updated with the setting of the

receive align frame bit in status register 2 (SR2.6). The host can use the SR2.6 bit to know when to read

the RAF and RNAF registers. It has 250ms to retrieve the data before it is lost.

On the transmitter, data is sampled from the TAF and TNAF registers with the setting of the transmit

align frame bit in status register 2 (SR2.3). The host can use the SR2.3 bit to know when to update the

TAF and TNAF registers. It has 250µs to update the data or else the old data is retransmitted. Data in the

Si bit position is overwritten if either the framer is programmed (1) to source the Si bits from the TSER

pin, (2) in the CRC4 mode, or (3) to have automatic E-bit insertion enabled. Data in the Sa-bit position is

overwritten if any of the TCR.3 to TCR.7 bits is set to 1. Please see the register descriptions for TCR for

more details.

RAF

Receive Align Frame Register

28 Hex

Bit 7 6 5 4 3 2 1 0

Name Si 0 0 1 1 0 1 1

NAME BIT FUNCTION

Si 7 International Bit

0 6 Frame Alignment Signal Bit

0 5 Frame Alignment Signal Bit

1 4 Frame Alignment Signal Bit

1 3 Frame Alignment Signal Bit

0 2 Frame Alignment Signal Bit

1 1 Frame Alignment Signal Bit

1 0 Frame Alignment Signal Bit