Commodore VIC-20 Programmer's Reference Manual page 273

KERNAL ENTRY
CLOSE (SFFC3)—See Section 3 for more information on entry
and exit conditions.
NOTE
Care should be taken to ensure all data is transmitted before
closing the channel. A way to check this from BASIC is:
100 IF ST-0 ANO (PEEK(37151) AND 64)= 1 GOTO 100
110 CLOSE if
Table 4-1. USER-PORT LINES
(6522 DEVICE #1 loc S9110-911F)
PIN 6522 IN/
ID ID DESCRIPTION EfA ABV OUT
MODES
c
D
E
F
H
J
K
L
B
M
A
N
PB0
PB1
PB2
PB3
PB4
PBS
PB6
PB7
CB1
CB2
GND
GND
RECEIVED DATA
REQUEST TO SEND
DATA TERMINAL READY
RiNG INDICATOR
RECEIVED LINE SIGNAL
UNASSIGNED
CLEAR TO SEND
DATA SET READY
RECEIVED DATA
TRANSMITTED DATA
PROTECTIVE GROUND
SIGNAL GROUND
(BB) Sin IN 1 2
(CA} RTS OUT 1*2
(CD)DTROUT1*2
(CE) Rl IN 3
(CF) DCD IN 2
( } XXX IN 3
(CB) CTS IN 3
(CC) DSR IN 2
(BB) Sin IN 1 2
(BA) Sout OUT 1 2
(AA) GND 1 2
(AB) GND 1 2 3
MODES
1)— 3-LINE INTERFACE (Sin,Sout,GND)
2) —X-LINE INTERFACE (Full handshaking)
3)—USER AVAILABLE ONLY {Unused/unimplemented in code,;
*—These lines are held high during 3-LINE mode.
"Note; PB6 CLEAR TO SEND is not implemented and must
be read with a short machine language routine.
257