Page 2.75
CIRCUIT DESCRIPTION
Keyboard
Keyboard
General
The keyboard circuits are designed around the 8041A univer-
sal peripheral interface (UPI) at U204. This IC is a dedicated
8-bit microcomputer with internal RAM and ROM. The RAM
is 64 x 8 bits while the ROM is 1024 x 8 bits.
The pin-out of the 8041A is described in the following para-
graphs. (For more information, see the 8041A data sheet in
Appendix C, Pin-Out Description.)
DO-D7, pins 12-19 (data bus). These are 3-state, bidirectional
data bus lines used to interface the UPI to the Computer data
bus. The CPU uses this bus to read the code of the pressed
key, read UPI status information, and to write command words
to the UPI.
CS, pin 6 (chip-select line). When the CPU addresses the
keyboard circuits at ports OF4H and OF5H, the I/O port de-
coder asserts line KEYBDSEL. This activates U204.
AO, pin 9 (address line 0). This is an address input used
by the Computer to indicate whether the byte transfer to DO-
D7 is data (A0
=
0) or a command (A0
=
1). This signal is de-
rived from the buffered address line 0 (BAO) from U161, pin
18.
RD, pin 8 (read data line). When this line is asserted, the
UPI transfers its internal data to the DO-D7 lines. The CPU
can then load this data into its accumulator.
WR, pin 10 (write data line). The CPU places data on pins
DO-D7 of the UPI. WR is then asserted by the CPU to load
the data into U204.
RESET, pin 4 (reset input line). This line resets the UPI's
status flip-flops and sets the program counter to 0.
Содержание Z-100 Series
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