Sharp MZ-5500 - Page 49

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6-3. Use of DMA channel 3
For the MZ-5500/5600 series, four DMA channels are provided standard. Since
the channel s 1 and 2 are already used by the machine, channels 0 and 3 are .
open [or the r/o slot. However, the channel 0 is used for the hard disk
iIlterfac e and the channel 3 is reserved for the standard floppy disk
interface.
The channel 3, hOHever, permits multiple-DMA up to eight levels (Table
below) . Attention must be paid to the following conditions when performing
direct data transfer with the main memory by me ans of DHA.
h
------
eh
0
Hard disk interface
Ch 1
MFD interface
~
Ch 2
Main memory refresh
~
Ch
3
A
Reserved r/o
AEH
to OlH
B
Reserved r/o AEH to
02H
C
SFD interface, MFD interface r/o AEl1 to .
04H
D
Reserved
r/o
AEH
to 08H
E
Reserved
1/0 AEH
to
lOH
F
Reserved
1/0
AEH
to 20H
G
Reserved r/o AEH to
40H
H
User
1/0 AEH
to 80H
1) Hardware
(1) Channel 3H is used [or the D~~ channel.
(2) Only byte transfer mode is applicable for the DMA transfer.
(3) DREQ3 (channel 3 DH.J\ request) must be outputted by the open collector as
it is wired-OR.
(4) Provide an output port to the bit 7 of the 1/0 address OAEH to permit
' input through the bit 7 of the r/o address OAFH.
(5) DR E Q3 and DACK3 are gated by the above output port.
(6) DREQ3 must be maintained active until DACK3 is returned.
(7) System data bus, D8 - D1S, must be pulled up with a proper resistance.
(8) Some means must be provided to know a DMA termination (interrupt, for
instance).
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