Measurement Computing Serial488A - Manual (Page 35)

3.1
Controller Operation
3.1 Controller Mode (Serial to IEEE) Operation
The IEEE Controller mode allows a serial RS-232 or RS-422 host device to
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 Serial488A 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 Serial488A will continue to
send data from it to the IEEE bus device. If the serial input buffer becomes emptied,
the Serial488A will command the IEEE bus device to talk if one of the talk back
features is enabled. This allows the Serial488A 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 Serial488A addresses the IEEE bus device to talk it uses the following
bus sequence:
ATN•UNL,MLA,TAG,*ATN
The Serial488A 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.