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

Chapter 3 77

Common Device Control Functions

Altering Terminal Deﬁceﬁles

Many of the asynchronous device control functions performed most

commonly are accomplished through the use of the FCONTROL

intrinsic. FCONTROL has often been referred to as the workhorse of

the ﬁle system intrinsics. The examples that follow illustrate how

FCONTROL can be used to alter the characteristics of data

transmission to and from a terminal, or to alter device control settings.

The syntax of FCONTROL is shown below:

I16V I16V *

FCONTROL(filenum,controlcode,param);

FCONTROL accesses speciﬁc deviceﬁles through their ﬁle numbers, as

speciﬁed in the ﬁlenum parameter. The function performed by a

particular call to FCONTROL is determined by the controlcode

parameter, as is the meaning and use of param. For some controlcode

values param has no meaning; in these cases param must be coded as

a dummy value to satisfy the requirements of the intrinsic.

See Chapter 8, “Intrinsics Reference,” for a list of the controlcode

values most useful for the control of asynchronous devices and for

information on how param is used for each of the controlcode values

described.

Completion status for each FCONTROL call is indicated through

condition codes. See Chapter 2, “Controlling Asynchronous Devices

Programmatically,” for more information on condition codes.

FCONTROL must be called before any data transfer activity in order to

have any effect on how that activity occurs. In many cases you will need

to use a series of FCONTROL calls to set all of the characteristics

desired for a particular transaction. The code fragments that follow

illustrate the use of a number of FCONTROL functions.

NOTE

An alternative to the FCONTROL intrinsic is provided by the

FDEVICECONTROL intrinsic, which is described in this manual. The

code segments shown in this chapter, however, demonstrate only the

use of FCONTROL.

Specifying an AEOR Character

Specifying an AEOR Character Figure 3-6 shows how FCONTROL may

be used to alter the way in which a read issued against a terminal can

be terminated. A controlcode value of 25 is used, which designates

that a character, speciﬁed through the call, is to be accepted as an

Additional End-of-Record (AEOR) character. In this case, an asterisk is

designated as the AEOR character.