Measurement Computing Micro 488/EX rev.2.1 - Manual (Page 165)

Section 6 Controller Pass-Thru Operation
6.1
Controller Pass-Thru Operation
6.1 Introduction
The Controller Pass-Thru mode allows a serial RS-232 or RS-422 host device to
transparently send data to a single IEEE bus peripheral or to multiple peripherals if
they occupy the same bus address. Applications include interfacing a listen-only or
addressable IEEE printer/plotter to a serial printer port.
Once the Micro488/EX has initialized itself after power-on, it waits for serial
input data. When received, it addresses the selected IEEE device to listen with the
following bus sequence:
ATN•UNL,MTA,LAG,*ATN
The data received from the serial host is placed into a circular serial input buffer.
Simultaneously, characters are removed from that buffer and sent to the IEEE bus
device. The serial terminator(s), if present, are not sent. Instead, the IEEE terminators
are substituted and sent in their place.
So long as the serial input buffer is not empty, the Micro488/EX will continue to
send data from it to the IEEE bus device. If the serial input buffer becomes emptied,
the Micro488/EX will command the IEEE bus device to talk if the talk back feature is
enabled. This allows the Micro488/EX to be used as a controller with devices, such as
plotters or instruments, that return status and other information to the host computer.
When the Micro488/EX addresses the IEEE bus device to talk it uses the
following bus sequence:
ATN•UNL,MLA,TAG,*ATN
The Micro488/EX then accepts data from the IEEE device and returns it to the
host until the last selected IEEE terminator is detected. The IEEE bus terminators are
replaced by the serial terminators and these are then sent to the serial host.