SAB82538 Datasheet, PDF (62/253 Pages) Infineon Technologies AG – ICs for Communications

SAB 82538
SAF 82538
2.3.2.2 Half-Duplex SDLC-NRM Operation
The LAP controllers of the eight serial channels can be configured to function in a half-
duplex Normal Response Mode (NRM), where they operate as a slave (secondary)
station, by setting the NRM bit in the XBCH register of the corresponding channel.
In contrast to the full-duplex LAPB/LAPD operation, where the combined (primary +
secondary) station transmits both commands and responses and may transmit data at
any time, the NRM mode allows only responses to be transmitted and the secondary
station may transmit only when instructed to do so by the master (primary) station. The
ESCC8 gets the permission to transmit from the primary station via an S-, or I-frame with
the poll bit (p) set.
The NRM mode can be profitably used in a point-to-multipoint configuration with a fixed
master-slave relationship, which guarantees the absence of collisions on the common
transmit line. It is the responsibility of the master station to poll the slaves periodically
and to handle error situations.
Prerequisite for NRM operation is:
q Auto mode with 8-bit address field selected
MODE: MDS1, MDS0, ADM = 000
q External timer mode
MODE: TMD = 0
q Same transmit and receive addresses, since only responses can be transmitted, i.e.
XAD1 = XAD2 = RAL1 = RAL2 (address of secondary)
Note: The broadcast address may be programmed in RAL2 if broadcasting is required.
In this case RAL1 and RAL2 are not equal.
The primary station has to operate in transparent SDLC mode.
Reception of Frames
The reception of frames functions similarly to the LAPB/LAPD operation (see 2.3.2.1).
Transmission of Frames
The ESCC8 does not transmit S-, or I-frames if not instructed to do so by the primary
station via an S-, or I-frame with the poll bit set.
The ESCC8 can be prepared to send an I-frame by the CPU by issuing an XIF command
(via CMDR) at any time. The transmission of the frame, however, will not be initiated by
the ESCC8 until reception of either an
q RR, or
q I-frame
with a poll bit set (p = 1).
Semiconductor Group
62