Measurement Computing GPIB-488.2 - Manual (Page 7)

GPIB 488.2 Porting Guide 978492 Introduction 1-5
Listener - A listener is any device which is able to receive data when properly addressed. There
can be up to 14 active listeners on the bus concurrently. Some devices can also be a talker or
controller; however, only one of these functions can be performed at a time.
Talker - A talker is a device which can transmit data over the bus when properly addressed.
Only one device can transmit at a time. Some devices can also be a listener or controller;
however, only one of these functions can be performed at a time.
Comparing IOtech GPIB with MCC GPIB 488.2 Commands
Chapter 2 of this guide consists of tables which list commands in alphabetical order. The first
table is for looking up IOtech commands and cross-referencing them to associated MCC GPIB
488.2 commands. For example, when looking up IOtech’s CheckListener we will see that
FindLstn is the associated MCC command.
IOtech GPIB Command Associated MCC GPIB 488.2 Command(s)
CheckListener FindLstn
A second set of tables is for looking up MCC commands and cross-referencing them to
associated IOtech commands.
MCC 488.2 addresses contain two bytes packed into a word. The low byte is the primary
address and the high byte is the secondary address. If secondary addressing is not used, then the
high byte should be zero.
High Byte: Secondary Address (0, or 96-126)
Low Byte: Primary Address: (0-30)
MCC 488.2 routines use a board address as the first argument (typically zero), instead of a
handle.
For both IOtech and MCC commands, this porting guide includes Syntax and Usage Notes. It
also includes an example in C language, for MCC 488.2 routines.
In the following text we will look briefly at IOtech’s CheckListener command and MCC’s
related FindLstn command.
IOtech
CheckListener: INT WINAPI CheckListener(DevHandleT devHandle,
BYTE primary, BYTE secondary);
devHandle refers to either an IEEE 488 hardware interface or an external device.
If devHandle refers to an external device, the CheckListener command acts
on the hardware interface to which the external device is attached.
primary is the primary bus address to check for a Listener (00 to 30)
secondary is the secondary bus address to check for a Listener (00 to 31).
For no secondary address, a -1 must be specified
Bus States: ATN•UNL, LAG, (check for NDAC asserted)