Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

98 Chapter4

Using FDEVICECONTROL

Examples

Specifying an End-of-Record Character

You can change the character that will be recognized as the

end-of-record character for a device by specifying a control directive of

39 and passing the desired character in buffer. This

FDEVICECONTROL is effective in either standard and transparent

editing mode. Note that the call does not alter the editing mode in effect

for the device; it simply changes the character that will signal the end

of a record for that device. This capability is not available through any

FCONTROL function.

You might want to use this capability, for example, to make it possible

for carriage returns to be passed in your data without enabling binary

editing mode and without modifying the processing of any other special

character. Only the end-of-record character is affected by this control

directive.

A notable characteristic of this use of FDEVICECONTROL is that the

value of the new end-of-record character must be passed in the high

order byte of the buffer parameter. The low order byte is not used with

this control directive. (Two other FDEVICECONTROL control

directives, 40 and 41, also require that the value be passed in the high

order byte.)

In Figure 4-3, FDEVICECONTROL is used to change the end-of-record

character to a bracket (]). Again, the value of the character is speciﬁed

through the Pascal/iX ord function and is then multiplied by 256 to

place it in the high order byte. Read/Write access is set to Write only for

the call, so the previous EOR character will not be returned to the

program.

To return to normal end-of-record processing, call this

FDEVICECONTROL again, specifying a null value as the EOR

character. The EOR character will be reset to the default character,

which is the carriage return. If you were processing in transparent

mode prior to changing the EOR character, and want to return to using

the EOR character that you speciﬁed in the call that established

transparent mode, you need to explicitly reset the EOR to that

character.