Page 2.91
CIRCUIT DESCRIPTION
If U179 pin 11 is asserted, section A of decoder U157 is
selected. It decodes address lines BA1 and BA2 to enable
t he interrupt ports, 8259ACSS and 8 2 59ACSM, o r t h e
keyboard port, KEYBDSEL.
If U179 pin 10 is asserted, section B of decoder U157 is
selected. It decodes address lines BA2 and BA3 to enable
one of the following ports:
6821ACSS. The parallel port, U114.
8253CS. The timer port, U160.
EPCIACS. Serial port A.
EPCIBCS. Serial port B.
If the keyboard, serial port A, or serial port B is selected,
pin 9 of U179 also goes low. This line is further decoded
by U222 to enable U241 whenever the CPU reads data from
one of these ports.
Содержание Z-100 Series
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