3.1.2 Output Port Handshake Lines (oDAV and oBusy)
The Output Data Available (oDAV) handshake line is an output line sourced by the
Digital488HS/32. The Output Port Busy (oBusy) handshake line is an input that is
sensed by the Digital488HS/32.
Data are not written to the output port while oBusy input is active. When oBusy
becomes inactive, all 17 bits of data, including oEND, are presented to the output
lines. 125 ns later, oDAV is forced active. In the 8-bit mode the first byte port content
is not specified.
Once the external device has sensed the assertion of oDAV, it must latch the data and
then assert oBusy for at least 150 ns. The external device must unassert oBusy when
it is ready for more data.
First Byte
Second Byte
oEnd
oDAV
oBusy
>125 ns
1) When oBusy input line is unasserted, the Digital488HS/32 puts data on the
output port.
2) The Digital488HS/32 waits at least 125 ns, then asserts oDAV.
3) The external device should then assert oBusy and latch the data.
4) oBusy must remain asserted until 150 ns have elapsed or oDAV becomes
unasserted.
5) The external device unasserts oBusy preparing for next transfer.
Output Port Timing Diagram
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