Page DD

CIA 2

Address	Name	Bit 7	Bit 6	Bit 5	Bit 4	Bit 3	Bit 2	Bit 1	Bit 0	Description
DD00	CIA2PRA	SBDI	SBCI	SBDO	SBCO	SBAO	TXD/PA2	VICMEM^[]		Data Port A^[1,2,3]
DD01	CIA2PRB	PB7 DSR	PB6 CTS	PB5 UPJ	PB4 DCD	PB3 RI	PB2 DTR	PB1 RTS	PB0 RXD	User Port PB0-7^[4]
DD02	CIA2DDRA	DDA7	DDA6	DDA5	DDA4	DDA3	DDA2	DDA1	DDA0	Data Direction Port A
DD03	CIA2DDRB	DDB7	DDB6	DDB5	DDB4	DDB3	DDB2	DDB1	DDB0	Data Direction Port B
DD04	CIA2TIMAL	TIMAL								Timer A Low byte
DD05	CIA2TIMAH	TIMAH								Timer A High byte
DD06	CIA2TIMBL	TIMBL								Timer B Low byte
DD07	CIA2TIMBH	TIMBH								Timer B High byte
DD08	CIA2RTCT	RTCT								Real time clock 1/10s
DD09	CIA2RTCS	RTCS								Real time clock seconds
DD0A	CIA2RTCM	RTCM								Real time clock minutes
DD0B	CIA2RTCH	RTCH								Real time clock hours
DD0C	CIA2SR	SR								Shift register
DD0D	CIA2ICS	NMI^[14] Source	Always 0 Unused		NMI Flag^[15] IntRel	SDR IntRel	Alarm IntRel	UTB IntRel	UTA IntRel	Interrupt Control & Status Read top, Write bottom
DD0E	CIA2CTA	RTC^[5]	SRC^[6]	TSRC^[7]	Load^[8]	RES^[9]	OVFL^[10]	UNFL1^[11]	START	Control Timer A
DD0F	CIA2CTB		TCOUNT^[13]		Load^[8]	RES^[9]	OVFL^[10]	UNFL2^[12]	START	Control Timer B

Multiple address ranges

CIA2 is mapped to addresses 0xDDxx but only occupies 16 bytes. Referencing any address from 0xDD1x…0xDDFx will mirror those at 0xDD0x.

SBxx Serial Bus, D=Data, C=Clock, A=Attention, I=In, O=Out
Bit 2 is RS232 TXD output or the userport PA2 (Pin M)
Bits 0 & 1 VIC-II memory base, %00 = Bank 3 0xC000-0xFFFF, %01 = Bank 2 0x8000-0xBFFF, %10 = Bank 1 0x4000-0x7FFF, %11 = Bank 0 0x0000-0x3FFF
Port B is the user port data, either 8 I/O pins or RS232
RTC 0=60Hz 1=50Hz
Shift register direction SP pin 0=read, 1=write
TSRC 0=count system cycles, 1=positive slope at CNT pin
1 = Load latic into the timer once
0 = Timer restart after underflow (latch reloaded), 1 = timer stops after underflow
0 = Timer overflow, port B bit 6 high 1 cycle, 1 = underflow, port B bit 6 inverted
1 = Indicates timer underflow at port B bit 6
1 = Indicates timer underflow at port B bit 7
Timer counts: %00 System cycle, %01 +ve slope CNT-pin, %10 Timer A underflow, %11 Timer A underflow if CNT-pin high
CIA-2 is connected to the NMI line
NMI Signal occured at FLAG-pin RS232 data received