Measurement Computing Digital488 - Manual (Page 9)

Section 1 Introduction
1.1
Introduction
1.1 General Description
The Digital488 is a digital input and output interface to the IEEE 488 bus.
Each unit has 40 TTL level digital I/O lines, which are divided into 5 eight-bit ports.
Each port is software programmable as input or output. The Digital488OEM is a
board level interface with the same capabilities as the Digital488. All descriptions in
this manual refer to both products unless otherwise stated. When the model number
Digital488 is used in this manual, Digital488OEM is also implied.
The Digital488 has several features which give it versatile interface
capability. A trigger output signal is asserted on the Group Execute Trigger (GET)
command. Edge-triggered inputs can generate a Service Request on the bus. Six data
formats are software programmable, including ASCII hexadecimal, ASCII character,
ASCII binary, binary, high speed binary and ASCII decimal. There are also
individual bit set and bit clear commands. Programmable terminators are provided
to facilitate interfacing to various controllers.
A status mode enables the controller to interrogate the programmed status of
the Digital488 at any time. A self-test is initiated at power-on which checks for
proper RAM and ROM operation.
When addressed to talk, the Digital 488 will output data from all forty bits or
a selected 8 bit port. When addressed to listen, the unit will input data and
programming information from the controller, and output the data to the appropriate
I/O port.