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ZiLOG
&/#ꢄ+ꢃ1ꢄ#&&4'55ꢄ4')+56'4
#NV'ꢆꢄThe #NV' bit should be set only when both DMA
channels are programmed for the same I/O source or I/O
destination. In this case, a channel end condition (byte count
= 0) on channel 0 sets bit 6 (#NV%), which subsequently
enables the channel 1 request and blocks the channel 0
request. Similarly, a channel end condition on channel 1
clears bit 6 (#NV%), which then enables the channel 0 request
and blocks the channel 1 request. For external requests, the
request from the device must be routed or connected to both
the &4'3ꢀ and &4'3ꢄ pins.
The DMA I/O Address Register specifies the I/O device for
channel 1 transfers. This address may be a destination or
source I/O device. +#4ꢄ. and +#4ꢄ* each contain 8 address
bits. The most significant byte identifies the Request Hand-
shake signal and controls the Alternating Channel feature.
&/#ꢄ+ꢃ1ꢄ#FFTGUUꢄ4GIKUVGTꢄ%JCPPGNꢄꢁꢄ.QY
/PGOQPKEꢄ+#4ꢁ.
#FFTGUUꢄꢇ$*
#NV%ꢆꢄIf bit (#NV') isꢅ0, the #NV% bit has no effect. When bit
7(#NV') is 1 andthe #NV% bit isꢅ0, the request signal selected
bybitsꢂ ꢀisnotpresentedtochannel1;however, thechan-
nel 0 request operates normally. When #NV' is 1 and #NV%
is 1, the request selected by 5#4ꢄꢆ ꢄꢁ or ꢄꢆ ꢄꢁ is
not presented to channel 0; however, the channel 1 request
operates normally. The #NV% bit can be written by software
to select which channel should operate first; however, this
operation should be executed only when both channels are
stopped (both &'ꢄ and &'ꢀ are ꢀ).
(KIWTG ꢈꢀꢆ &/#ꢄ+ꢃ1ꢄ#FFTGUUꢄ4GIKUVGTꢄ%JCPPGNꢄꢁꢄ.QY
&/#ꢄ+ꢃ1ꢄ#FFTGUUꢄ4GIKUVGTꢄ%JCPPGNꢄꢁꢄ*KIJ
/PGOQPKEꢄ+#4ꢁ*
#FFTGUUꢄꢇ%*
4GSꢁ5GNꢆꢄIf bit &+/ꢄ in the &%06. register is 1, indicating
an I/O source, the following bits select which source hand-
shake signal should control the transfer:
(KIWTG ꢈꢏꢆ &/#ꢄ+ꢃ1ꢄ#FFTGUUꢄ4GIKUVGTꢄ%JCPPGNꢄꢁꢄ*KIJ
ꢀꢀꢀ
ꢀꢀꢄ
ꢀꢄꢀ
1VJGT
&4'3ꢄꢅRKP
#5%+ꢀꢅ4&4(
#5%+ꢄꢅ4&4(
4GUGTXGFꢇꢅFQꢅPQVꢅRTQITCO
&/#ꢄ+ꢃ1ꢄ#FFTGUUꢄ4GIKUVGTꢄ%JCPPGNꢄꢁꢄ$
/PGOQPKEꢄ+#4ꢁ$
#FFTGUUꢄꢇ&*
If &+/ꢄ isꢅ0, indicating an I/O destination, the following
bits select which destination handshake signal should con-
trol the transfer:
$KV
ꢊ
ꢍ
ꢂ
ꢄ
ꢀ
ꢁ
ꢏ
ꢎ
#NV%
#NV'
4GSꢅꢄꢅ5GN
ꢀꢀꢀ
ꢀꢀꢄ
ꢀꢄꢀ
1VJGT
&4'3ꢄꢅRKP
#5%+ꢀꢅ6&4'
#5%+ꢄꢅ6&4'
4GUGTXGFꢇꢅFQꢅPQVꢅRTQITCO
(KIWTG ꢐꢂꢆ &/#ꢄ+ꢃ1ꢄ#FFTGUUꢄ4GIKUVGTꢄ%JCPPGNꢄꢁꢄ$
&5ꢀꢀꢁꢀꢀꢂꢃ</2ꢀꢂꢀꢀ
2ꢅ4ꢅ'ꢅ.ꢅ+ꢅ/ꢅ+ꢅ0ꢅ#ꢅ4ꢅ;
ꢏꢊ
ZILOG [ ZILOG, INC. ]
