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QPC513 Enhanced Serial Data Interface card Page 843 of 894
Circuit Card Description and Installation
The QPC513 ESDI card is an intelligent controller. The local
micro-processor performs all of the overhead associated with synchronous
data transfer. The system processor passes data to the ESDI card processor a
byte at a time using conventional memory reads and writes. The ESDI card
processor stores the data in a RAM cache on the ESDI card, and passes it to
the synchronous communication chip in blocks using Direct Memory Access
(DMA) techniques.
Synchronous communication
The ESDI cards supports LAPB, a subset of the HDLC synchronous protocol.
A description of the LAPB protocol is shown in Appendix A, LAPB data link
protocol on page 889.
The HDLC data link is a bit-oriented protocol. The information data bits are
transmitted transparently across the link in packets. The maximum length of
the information field for these packets is 128 octets, where an octet consists
of 8 bits.
The characteristics of the synchronous communication ports are shown in
Table 261.
Table 261
Characteristics of synchronous ports (Part 1 of 2)
Characteristics Description
Duplex mode half, (full)
Data rate (bps) 1200, 2400, (4800), 9600,
19200, 48000, 56000, 64000
Clock (internal), external
Data Link Level LAPB protocol
SL-1 address
(1), 3
Note 1: * See the Configuration Record (LD 17) in Software Input/Output:
Administration (553-3001-311) to modify the link control system
parameters and performance thresholds.
Note 2: The values in parentheses are the default.