Dma Transfers - HP 9835A Programming Manual

I/O Handling
149
DMA Transfers
OMA transfers are accomplished with six distinct actions.
First, the Isr _access utility is used to obtain access to the OMA channel and to set up the ISR
linkage used when the transfer terminates.
Second, the direction is set using an SOO or SOl instruction. If no direction is set, then any
previous setting of the direction prevails.
Third, the appropriate values are stored into the OMA registers.
Fourth, the OMA requests are enabled using the instruction -
Fifth, a "Start OMA" command is given to the interface using programmed I/O. With the
98032 interface, this command is the value 3208 using the Primary Control register (R5-0ut).
Finally, when the OMA transfer is complete, the interface generates an interrupt which causes
the processor to branch to the designated ISR. This ISR should disable the card, and then
disable the OMA mode with the instruction -
: i i
111
The following is part of an ISR which demonstrates a typical set-up for a OMA inward transfer
(in this case lK words placed into a buffer in memory) -
.. ······:i:::i
'._ ..... Ar 1:·
'j
:::.('~
::'::"' ...
i:, .. :: ':-:':::.:::;.
:-'1"'-
"ro'
::::;c . .
:~::.,
....