Commodore PET User Manual page 357

Table 6-2. PET Memory Map (Rev. 3 ROMs) (Continued)
Memory Address Sample Value
Decimal
59456
59457
59458
59459
59460-59461
59462-59463
59464
59465
59466
59467
59468
59469
59470
59471
Hexadecimal
E840
E841
E842
E843
E844-E845
E846-E847
E848
E849
E84A
E84B
E84C
E84D
E84E
E84F
Decimal
223
255
30
o
29241
65535
147
217
o
o
14
o
128
255
Hexadecimal
DF
FF
lE
00
7239
FFFF
93
D9
00
00
OE
00
80
FF
Description
Parallel User Port VIA
(59456-59471 )
1/0 Port B
207=#2 cassette motor on
223=#2 cassette motor off
WAIT 59456.23.23 waits for vertical
retrace of display
Bit 1
~PB1
INFRD on IEEE connector)
output line
Bit
3~PB3IATN
on IEEE connector)
output !ine
1/0 Port A with handshaking
Data Direction register for 1/0 Port B
Data Direction register for
1/0
Port A
For each bit 1 ~outpul. O~input
~O ail input
~255 ail output
(Law. high arder) Read Timer
1.
Counter;
write ta Timer 1 Latch and (high byte)
initiate count
(Law. high arder) Read Timer 1 Latch
Read Tlmer 2 Counter low byte and reset
mterrupl. write ta Timer 2 low byte
PEEK (59464) Clock decrements every
microsecond
POKE 59454.n sets SR rate of shift from
hlgh
(n~O)
ta low
(n~255)
for musIc from
User Port
Read Timer 2 Counter high byte; write ta
Timer 2 high byte and reset interrupt
PEEK (59465) Clock decrements every
millisecond
Seriai 1/0 Shift register (SR)
POKE 59466. 15 or 85 ta generate
Square wave output at CB2 for playing
music from User PorI.
Auxiliary Control register
= 16 Sets SR ta free-running mode for
music from User Port
~O
for proper operation of tape drive
Peripheral Control register
~
12 for graphics on shifted
characters
=14 for lower-case letters on shifted
characters
Interrupt Flag register
Interrupt enable register
1/0
Port A without handshaking
61440-61621
344
FOOO-FOB5
Page 241-256 Operating System 161440-65535)
Monitor messages