User`s guide

164 DC 900-1340I
BSC Programmer’s Guide
0 none No data parity, no control character parity
1 odd No data parity, odd control character parity
2 even No data parity, even control character parity
6.8 Transmission Block Size Option (8)
The BSC software has transmission buffers fixed at 4,096 bytes. Each link has one trans-
mit buffer and one receive buffer. You can define the maximum amount of the 4,096
bytes that the BSC software can transmit as one block on the communication line by
setting the transmission block size from 64 to 4,096 bytes. The BSC software, however,
can receive blocks up to 4,096 bytes regardless of the setting of this option. See
Section 2.3.4 on page 40 for more information on transmission blocks.
The size of the transmission block includes the bisynchronous text control characters as
well as the data characters. For example, a transmission block size of 512 bytes consists
of 510 bytes of data plus two control characters (STX and ETX). SYN, DLE, PAD, and
BCC characters are not included in the transmission block size count. The BSC software
automatically inserts all control characters in the transmission block. If the remote sta-
tion sends a transmission block that is larger than 4,096 bytes, the BSC software sends a
NAK response to the transmission and returns the
DLI_ICP_ERR_BUF_OVERFLOW buffer
overrun error to the client along with all the data which was successfully received.
The size of message buffers from the client is independent of the transmission block
size. The ICP message buffer size is controlled by the Set ICP Message Buffer Size com-
mand (Section 5.4.1.3 on page 119). Messages to be transmitted that are greater than
the transmission block size are broken into smaller messages and sent separately.
For messages received on the communication line, the ICP message buffer size
(Section 5.4.1.3 on page 119) is the maximum size that can be received; otherwise, the
DLI_ICP_ERR_BUF_OVERFLOW error code is sent to the client application.
To set this option using the DLI configuration file, use the transBlkSize parameter; for
example,
transBlkSize = 512. See Table 7–2 on page 191.