User`s guide

90 DC 900-1339H

FMP Programmer’s Guide

4.14 Block Checking Option (20)

This option determines what characters are included in the block check character

(BCC) calculation on transmitted and received data blocks. If the received block check

character does not match the BCC value calculated by FMP, the

DLI_ICP_ERR_BAD_BCC

error code is returned to the client application. Block checking can be set to include or

exclude the leading FMP control character or can be disabled completely. It does not

apply to unstructured asynchronous lines (line mode options 2–5).

If the option is set to exclude, the BCC calculation starts with the ﬁrst data character fol-

lowing SOH. This is the normal FMP mode of BCC calculation.

If the option is set to include, the SOH is included in the BCC calculation for transmit-

ted and received data blocks.

If the option is set to disable, a block check character is still generated on transmit and

expected on receive, but the receive BCC comparison is not performed and each

received data block is sent to the client without regard to any possible error. The BCC

calculation is done on transmitted blocks as if the option is set to exclude.

If the line mode option (Section 4.18 on page 92) is set for the Bonneville feed, the FMP

software calculates the special two-byte Bonneville frame check sequence (FCS)

whether this option is set for include or exclude. However, if this option is set to disable,

the FMP software will not check the FCS of incoming packets and pass every packet to

the user without block check error.

Note

When transmitting non-transparent text, embedded SYN charac-

ters are not included in the outbound BCC calculation.

To set this option using the DLI conﬁguration ﬁle, use the

blockChecking parameter;

for example,

blockChecking = “exclFirst”. See Table 5–1 on page 104.