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/ꢁ6'ꢄꢌ/ꢁꢄ6GORQTCT[ꢄ'PCDNGꢍꢆꢄThis bit controls the tem-
porary assertion of the /ꢄ signal. It is always read back as
a 1 and is set to 1 during 4'5'6.
For example, when a control word is written to the Z80 PIO
to enable interrupts, no enable actually takes place until the
PIO sees an active /ꢄ signal. When /ꢄ6' =ꢅ1, there is no
change in the operation of the /ꢄ signal, and /ꢄ' controls
itsfunction. When /ꢄ6' =ꢅ0, the /ꢄ output isasserteddur-
ing the next opcode fetch cycle regardless of the state pro-
grammed into the /ꢄ' bit. This condition is only momen-
tary (one time) and it is not necessary to preprogram a 1
to disable the function (see Figure 10).
When /ꢄ' is set toꢅ0to accommodate certain external Z80
peripheral(s), those same device(s) may require a pulse on
/ꢄ after programming certain of their registers to complete
the function being programmed.
6
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1REQFGꢅ(GVEJ
(KIWTG ꢁꢂꢆ /ꢁꢄ6GORQTCT[ꢄ'PCDNGꢄ6KOKPI
+1%ꢄꢌ+ꢃ1ꢄ%QORCVKDKNKV[ꢍꢆꢄThis bit controls the timing of the
+143 and 4& signals. The bit is set to 1 by 4'5'6.
When +1% =ꢅ1, the +143 and 4& signals function the same
as the Z64180 (Figure 11).
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ZILOG [ ZILOG, INC. ]
