Z80180 Datasheet, PDF (118/326 Pages) Zilog, Inc. – Z8018x Family MPU

Z 8018x Fam ily
M PU Us e r M anual
103
Bit
Position Bit/Field R/W Value Description
2-0
R/W 000 DMA1 ext TOUT/DREQ
001 DMA1 ASCI0
010 DMA1 ASCI1
011 DMA1 ESCC
111 DMA1 PIA27-20 (P1284)
DMA Register Description
Bit 7
This bit must be set to 1 only when both DMA channels are set to take
their requests from the same device. If this bit is 1 (it resets to 0), the
TEND output of DMA channel o sets a flip-flop, so that thereafter the
device’s request is visible to channel 1, but not visible to channel 0. The
internal TEND signal of channel 1 clears the FF, so that thereafter, the
device’s request is visible to channel 0, but no visible to channel 1.
If DMA request are from differing sources, DMA channel 0 request is
forced onto DMA channel 1 after TEND output of DMA channel 0 sets
the flop-flop to alternate.
Bit 6
When both DMA channels are programmed to take their requests from
the same device, this bit (FF mentioned in the previous paragraph)
controls which channel the device’s request is presented to: 0 = DMA0, 1
= DMA l. When Bit 7 is 1, this bit is automatically toggled by the channel
end output of the channels.
UM005001-ZMP0400