Radio Shack TRS-80 - Page 14

COLOR COMPUTER
MEMORY
MAP
(Cont'd)
FF20-FF23 PIA
U4
FF20
BIT
=
CASSETTE DATA INPUT
BIT
1
=
RS-232
DATA OUTPUT
BIT2
=
6BITD/ALSB
BIT3=6BITD/A
BIT4
=
6BITD/A
BIT5=6BITD/A
BIT6=6BITD/A
BIT 7
=
6
BIT
D/A MSB
FF21
BIT0
BIT1
Control
of
the CD
RS-232
status
Input
1
F IRQ* to
CPU Disabled
-
F
IRQ* to
CPU Enabled
=
set flag on falling edge CD
1
=
set flag on rising edge CD
BIT 2
=
Normally
1
:
=
changes FF20to the data direction register
BIT 3
=
Cassette Motor
Control
:
=
OFF 1
=
ON
BIT
4
=
1 Always
BIT
5
=
1 Always
BIT
6 Not Used
. BIT 7
=
CD Interrupt Flag
FF22
FF23
BIT
=
RS-232 DATA INPUT
BIT 1
=
SINGLE
BIT SOUND OUTPUT
BIT
2=
RAM SIZE INPUT
LOW
=
4K
BIT 3
=
VDG CONTROL OUTPUT
BIT
4
=
VDG
CONTROL OUTPUT
BIT
5
=
VDG CONTROL OUTPUT
BIT
6
=
VDG
CONTROL OUTPUT
BIT 7
=
VDG CONTROL
OUTPUT
BIT0 I
1 Control of the Cartridge
BIT
1
J
Interrupt Input
j
=
sets f ,
ag
on
faMing
edge CART
«
1
=
sets flag on rising edge CART*
BIT
2
=
Normally
1:
=
changes FF22
to the data direction
register
BIT
3
=
Six BIT Sound Enable
BIT 4
=
1 Always
BIT
5
=1
Always
BIT
6
=
Not Used
BIT 7
=
Cartridge
Interrupt Flag
HIGH
=
16K
CSS
GM0& INT/EXT
GM1
GM2
A/G
0=
FIRQ*toCPU Disabled
1
=
FIRQ*toCPU Enabled
FF40- FFBF
NOT USED