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

92 Chapter4

Using FDEVICECONTROL

Syntax Description

While FDEVICECONTROL performs some of the same device control

functions performed by FCONTROL, the two intrinsics look very

different from each other when you use them in a program.

FCONTROL uses just three parameters, through which you specify a

deviceﬁle, deﬁne the control operation to be performed, and, depending

on the control operation, pass or receive speciﬁc information that may

be required for that operation.

FDEVICECONTROL requires the use of a greater number of

parameter values. For operations that can be performed by either

FCONTROL or FDEVICECONTROL, it is easier to use FCONTROL.

The following is the syntax for FDEVICECONTROL:

I16V UDS I16V I16V

FDEVICECONTROL(filenum,buffer,length,controlcode,

I16V U16V U16

parm1,parm2,fserrorcode);

FDEVICECONTROL is used for a variety of ﬁle control operations,

each of which is appropriate for controlling a speciﬁc type of deviceﬁle.

The controlcode parameter determines the control operation that will

be performed. The only control operation which effects asynchronous

deviceﬁles is controlcode value 192. It sends device control directives

to an asynchronous device.

Refer to Table 8-7 for a list of other valid controlcode values and the

operations they perform. For more information on these operations

refer to the MPE/iX Intrinsics Reference Manuals.

When controlcode is 192, parm1 determines the speciﬁc control

directive to be sent to the deviceﬁle. parm1 must contain one of the

control directive values speciﬁed in Chapter 4, “Using

FDEVICECONTROL.”

parm2 determines the Read/Write access to be imposed on the

directive. The Read/Write access setting must be valid for the control

directive speciﬁed in parm1. Set parm2 to 1 for Read access, 2 for

Write access, or 3 for both Read and Write access.

For example, if you were to call FDEVICECONTROL with

controlcode set to 192 and parm1 set to 57, which is the control

directive used to obtain the subsystem break character, you would need

to set parm2 to 1, since only Read access is allowed for that control

directive.

If, however, parm1 were set to 36, which is the control directive used to

deﬁne the backspace character, you could set parm2 to 1, 2, or 3. In this

case, setting parm2 to 1 would return the current backspace character