Measurement Computing Digital HS - Manual (Page 3)

Introduction
1.1 General Description
The Digital488HS/32 is a high speed IEEE 488 to digital I/O interface providing the
fastest possible communication between the IEEE 488 bus and 34 TTL compatible
digital I/O lines (17 inputs and 17 outputs). Both the input lines and the output lines
have an associated pair of handshake lines. The Data Available (iDAV and oDAV for
input and output respectively) line is driven by the data source to indicate that the
receiver should accept new data. The Busy (iBusy and oBusy for input and output
respectively) line is driven by the receiver to indicate that the source should not send
new data. Each handshake line is switch selectable for either active high or active low
operation.
The input and output ports are separated into one 8-bit (first byte) port and one 9-bit
(second byte) port. There are two separate switch selectable operating modes for both
the input and output data ports, 8-bit and 16-bit. In the 8-bit mode, 8-bit data are
transferred to or from the second byte port with the IEEE 488 bus control line EOI as
the 9th bit. In the 16-bit mode, the first eight bits of data are transferred to or from the
first byte port followed by the next eight bits with EOI to or from the second byte
port. The user connects the external I/O device to correspond to the desired byte
ordering (most significant byte first or least significant byte first). Both input and
output ports are separately switch selectable for either active high or active low
output data operation.
The output port provides switch selection for each bit of high or low on power-on,
reset, or clear.
There are two switch enabled conditions for which the Digital488HS/32 can request
service with SRQs: Output Port Empty and Input Port Full. This status can also
determined by Parallel Poll via switch selectable responses.
Some of the control lines available are:
oClear This output line provides an active 1µSec pulse upon
detection of the IEEE 488 multiline commands DCL and
SDC. This control line is switch selectable for either active
high or active low operation.