SNAX/APN Application Programming Manual

The CRT Interface
SNAX/APN Application Programming Manual—420111-001
2-6
Enhanced CDI Mode
Enhanced CDI Mode
Enhanced CDI mode functions in the same way as normal CDI mode except for one
additional feature.
When an application issues a WRITE procedure call, it can cause the enabling of the
CDI with a 3270 write command if the keyboard restore bit of the WCC byte is enabled.
The keyboard restore bit is found in the following 3270 write commands:
Write
Erase/Write
Erase/Write Alternate
The keyboard restore bit is also found in structured fields if the 3270 command is a write
structured field (WSF) command. The CRT protocol examines the following structured
fields, and, if any of the following are encountered, they will set CDI in the header in a
WSF command:
Outbound Text Header
Outbound 3270 Data Stream
Present Absolute Format
Present Relative Format
In the case of structured fields, the CDI is enabled when all of the following conditions
are true:
•
Any of the structured fields listed above are found in the outbound data stream
•
The keyboard restore indicator (bit 6 of the WCC byte within the structured field) is
enabled
•
The command (CMD) byte is any of the following: Write, Erase/Write, Erase/Write
Alternate
Enhanced CDI mode reduces time delay and eliminates the need for null RU
transmission. It thereby reduces the potential need for data reentry. For example, if an
application uses an initial WRITE procedure call to send a prompt to a device, the CDI
is set in the outbound RU. The subsequent READ procedure call does not result in
further SNA traffic.