Philips Semiconductors

Product specification

SCN2652/SCN68652

Multi-protocol communications controller (MPCC)

1995 May 01

15

Table 7.

Transmit Data/Status Register (TDSR) (R/W except TDSR15)

BIT

NAME

MODE

FUNCTION

00–07

TxDB

BOP/BCP

Transmit data buffer. Contains processor loaded characters to be serialized in TxSR and

transmitted on TxSO.

08

TSOM

Transmitter start of message. Set by the processor to initiate message transmission provided

TxE = 1.

BOP

TSOM = 1 generates FLAGs. When TSOM = 0 transmission is from TxDB and FCS

preset to 1’s.

BCP

respectively. When TSOM = 0 transmission is from TxDB and CRC generation (if specified)

begins.

09

TEOM

Transmit end of message. Used to terminate a transmitted message.

BOP

TEOM = 1 causes the FCS and the closing FLAG to be transmitted following the transmission

of the data character in TxSR. FLAGs are transmitted until TEOM = 0. ABORT or GA are

transmitted if TABORT or TGA are set when TEOM = 1.

BCP

or TxDB (IDLE = 0 or 1). Clearing TEOM prior to the end of CRC–16 transmission (when

TxBE = 1) causes TxSO to be marked following the CRC–16. TxE must be dropped before a

new message can be initiated. If CRC is not selected, TEOM should not be set.

10

TABORT

BOP

Transmitter abort = 1 will cause ABORT or FLAG to be sent (IDLE = 1 or 1) after the current

character is transmitted. (ABORT = 11111111)

11

TGA

BOP

Transmit go ahead (GA) instead of FLAG when TEOM = 1. This facilitates repeater

termination in loop mode. (GA = 01111111)

12–14

Not Defined

15

TERR

Read

only

Transmitter error = 1 indicates the TxDB has not been loaded in time (one character time–1/2

TxC period after TxBE is asserted) to maintain continuous transmission. TxU will be asserted

to inform the processor of this condition. TERR is cleared by setting TSOM. See timing

diagram.

BOP

ABORT’s or FLAG’s are sent as fill characters (IDLE = 0 or 1)

BCP

SYNC’s or MARK’s are sent as fill characters (IDLE = 0 or 1). For IDLE = 1 the last character

before underrun is not valid.