Philips Semiconductors

Product specification

SCN2652/SCN68652

Multi-protocol communications controller (MPCC)

1995 May 01

20

TRANSMIT UNDERRUN

TxC

DBEN2

SET TSOM

NOTES:

1.

TxU goes active relative to TxC falling edge if TxBE has not been serviced after n-1/2 TxC times (where n = transmit character length). TxU is reset on the TxC falling edge follow-

ing assertion of the TSOM command.

2.

An underrun will occur at the next character boundary if TEOM is reset and the transmitter remains enabled, unless the TSOM command is asserted or a character is loaded into

the TxDB.

TxU1

SD00070

Figure 15. Timing Diagrams (cont.)

RECEIVE – START OF MESSAGE

RxC

RxA

RxDA2

DBEN

1st CHAR READ

2nd CHAR READ

S/F3

RxE

NOTES:

1.

RxA goes high relative to falling edge of RxC when RxE is high and: a. A data character following two SYNC’s is in RxDB (BCP mode). b. Character following FLAG is in RxDB

(BOP primary station mode). c. Character following FLAG is in RxDB and character matches the secondary station address or all parties address (BOP secondary station mode).

2.

RxDA goes high on RxC falling edge when a character in RxDB is ready to be read. It comes up before RxSA and goes low on the falling edge of DBEN when RxDB is read.

3.

S/F goes high relative to rising edge of RxC anytime a SYNC (BCP) or FLAG (BOP) is detected.

1

1st CHAR READY

TO BE READ

2nd CHAR READY

TO BE READ

SD00071

Figure 16. Timing Diagrams (cont.)