Asynchronous Terminals and Printer Processes Programming Manual

PROCEDURE CALLS FOR ACCESSING TERMINALS
ATP6100 Operational Examples
• The BREAK key is pressed, and BREAK is enabled for the
terminal regardless of interrupt character checking or trans-
fer mode. On return from READ or WRITEREAD, nothing is
transferred into the buffer, 0 is returned in the count-read
parameter, and the condition code is CCL.
• Read termination on ETX is enabled, and an ETX character
followed by the designated number of checksum characters is
input. On return from READ or WRITEREAD, the buffer contains
the number of characters returned in the count-read parameter,
and the condition code is CCE. The last two or three
characters in the buffer are ETX and one or two checksum
characters.
• A parity, framing, data overrun, or modem error occurs.
• A 6530 ENQ/ACK protocol timeout occurs (6520 or 6530 block
mode only).
• GUARDIAN 90 detects a critical, file-system error.
ATP6100 OPERATIONAL EXAMPLES
The next few pages present examples of some typical requests
made by ATP6100 on behalf of an application. The intent is to
demonstrate in a general way how the I/O process-LIU interface
works and not to present an exhaustive description of the
interface.
Conversational Mode
When an application communicates with a terminal in conversa-
tional mode, it usually issues a prompt to fetch the operator's
input. The I/O process forwards the application request to the
LIU as a WRITEREAD request. During the read portion of the
WRITEREAD, the protocol module receives characters and acts upon
them as they are received. If a backspace is received from
a terminal that does not erase when backspaced, the protocol
module terminates the WRITEREAD and issues another WRITEREAD to
erase the previous character and obtain the rest of the input.
When the line termination character is received, the WRITEREAD
is terminated and the original request is also completed.
Figure 3-1 illustrates this dialogue.
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