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

Chapter 4 93

Using FDEVICECONTROL

Syntax Description

to your program, while setting it to 2 would actually change the

backspace character to whatever new character you pass in the call

(through the buffer parameter). Setting parm2 to 3 would both return

the previous value and change the backspace character to the new

value passed in the call.

Some control directives do not permit all possible values of parm2 to be

used with them. Table 8-8 lists the allowable parm2 access values for

each of the valid control directives that may be speciﬁed in parm1.

The ﬁlenum parameter speciﬁes the ﬁle number, as obtained through a

previous call to FOPEN or HPFOPEN, of the deviceﬁle on which the

control operation is to be performed.

The buffer parameter passes and returns the data associated with the

control directive being performed. For example, if the control directive

speciﬁed in parm1 is 3, which sets the line speed for a device, buffer

must contain the new linespeed setting (and will return the previous

speed setting if parm2 is set to Read/Write access).

The length parameter sets the length of buffer. Positive values

indicate the length in half words. Negative values indicate the length in

bytes. Usually length will be set to 1, indicating that buffer is 1 half

word long.

The fserrorcode parameter returns error information to your

program. If no error occurs during execution, fserrorcode contains a 0.

If an error occurs, fserrorcode returns the ﬁle system error code

corresponding to that error. You will need to call FCHECK for more

information about the error that occurred.