Table 6-1. User-Port Lines

(6526 DEVICE #2 Loc. $DD00-$DD0F)
PIN ID	6526 ID	DESCRIPTION	EIA	ABV	IN/OUT	MODES
C	PB0	RECEIVED DATA	(BB)	Sin	IN	1 2
D	PB1	REQUEST TO SEND	(CA)	RTS	OUT	1*2
E	PB2	DATA TERMINAL READY	(CD)	DTR	OUT	1*2
F	PB3	RING INDICATOR	(CE)	RI	IN	3
H	PB4	RECEIVED LINE SIGNAL	(CF)	DCD	IN	2
I	PB5	UNASSIGNED	( )	XXX	IN	3
K	PB6	CLEAR TO SEND	(CB)	CTS	IN	2
L	PB7	DATA SET READY	(CC)	DSR	IN	2
B	FLAG2	RECEIVED DATA	(BB)	Sin	IN	1 2
M	PA2	TRANSMITTED DATA	(BA)	Sout	OUT	1 2
A	GND	PROTECTIVE GROUND	(AA)	GND		1 2
N	GND	SIGNAL GROUND	(AB)	GND		1 2 3
MODES: 3-LINE INTERFACE (Sin,Sout,GND) X-LINE INTERFACE USER AVAILABLE ONLY (Unused/unimplemented in code.) * These lines are held high during 3-LINE mode.

[7] [6] [5] [4] [3] [2] [1] [0] (Machine Lang.-RSSTAT | | | | | | | +- PARITY ERROR BIT | | | | | | +----- FRAMING ERROR BIT | | | | | +--------- RECEIVER BUFFER OVERRUN BIT | | | | +------------- RECEIVER BUFFER-EMPTY | | | | (USE TO TEST AFTER A GET#) | | | +----------------- CTS SIGNAL MISSING BIT | | +--------------------- UNUSED BIT | +------------------------- DSR SIGNAL MISSING BIT +----------------------------- BREAK DETECTED BIT

Figure 6-3. RS-232 Status Register.