Der C64 hat zwei Bausteine des Typs MOS 6526; ersterer DC00h-DCFFh, zweiterer DD00h-DDFFh.

CIA 1
DC00	Data Port A (Keyboard, Joystick, Paddles, Light-Pen) 7-0 Write Keyboard Column Values for Keyboard Scan 7-6 Read Paddles on Port A / B (01 = Port A, 10 = Port B) 4   Joystick A Fire Button: 1 = Fire 3-2   Paddle Fire Buttons 3-0   Joystick A Direction (0-15)
DC01	Data Port B (Keyboard, Joystick, Paddles): Game Port 1 7-0   Read Keyboard Row Values for Keyboard Scan 7   Timer B Toggle/Pulse Output 6   Timer A: Toggle/Pulse Output 4   Joystick 1 Fire Button: 1 = Fire 3-2   Paddle Fire Buttons 3-0   Joystick 1 Direction
DC02	Data Direction Register - Port A
DC03	Data Direction Register - Port B
DC04	Timer A: Low-Byte
DC05	Timer A: High-Byte
DC06	Timer B: Low-Byte
DC07	Timer B: High-Byte
DC08	Time-of-Day Clock: 1/10 Seconds
DC09	Time-of-Day Clock: Seconds
DC0A	Time-of-Day Clock: Minutes
DC0B	Time-of-Day Clock: Hours + AM/PM Flag (Bit 7)
DC0C	Synchronous Serial I/O Data Buffer
DC0D	CIA Interrupt Control Register (Read IRQs/Write Mask) 7   IRQ Flag (1 = IRQ Occurred) / Set-Clear Flag 4   FLAG1 IRQ (Cassette Read / Serial Bus SRQ Input) 3   Serial Port Interrupt 2   Time-of-Day Clock Alarm Interrupt 1   Timer B Interrupt 0   Timer A Interrupt
DC0E	CIA Control Register A 7   Time-of-Day Clock Frequency: 1 = 50 Hz, 0 = 60 Hz 6   Serial Port I/O Mode Output, 0 = Input 5   Timer A Counts: 1 = CNT Signals, 0 = System 02 Clock 4   Force Load Timer A: 1 = Yes 3   Timer A Run Mode: 1 = One-Shot, 0 = Continuous 2   Timer A Output Mode to PB6: 1 = Toggle, 0 = Pulse 1   Timer A Output on PB6: 1 = Yes, 0 = No 0   Start/Stop Timer A: 1 = Start, 0 = Stop
DC0F	CIA Control Register B 7   Set Alarm/TOD-Clock: 1 = Alarm, 0 = Clock 6-5   Timer B Mode Select:         00 = Count System 02 Clock Pulses         01 = Count Positive CNT Transitions         10 = Count Timer A Underflow Pulses         11 = Count Timer A Underflows While CNT Positive 4-0   Same as CIA Control Reg. A - for Timer B
CIA 2
DD00	Data Port A (Serial Bus, RS-232, VIC Memory Control) 7   Serial Bus Data Input 6   Serial Bus Clock Pulse Input 5   Serial Bus Data Output 4   Serial Bus Clock Pulse Output 3   Serial Bus ATN Signal Output 2   RS-232 Data Output (User Port) 1-O VIC Chip System Memory Bank Select (Default = 11)
DD01	Data Port B (User Port, RS-232) 7   User / RS-232 Data Set Ready 6   User / RS-232 Clear to Send 5   User 4   User / RS-232 Carrier Detect 3   User / RS-232 Ring Indicator 2   User / RS-232 Data Terminal Ready 1   User / RS-232 Request to Send 0   User / RS-232 Received Data
DD02	Data Direction Register - Port A
DD03	Data Direction Register - Port B
DD04	Timer A: Low-Byte
DD05	Timer A: High-Byte
DD06	Timer B: Low-Byte
DD07	Timer B: High-Byte
DD08	Time-of-Day Clock: 1/10 Seconds
DD09	Time-of-Day Clock: Seconds
DD0A	Time-of-Day Clock: Minutes
DD0B	Time-of-Day Clock: Hours + AM/PM Flag (Bit 7)
DD0C	Synchronous Serial I/O Data Buffer
DD0D	CIA Interrupt Control Register (Read NMls/Write Mask) 7   NMI Flag (1 = NMI Occurred) / Set-Clear Flag 4   FLAG1 NMI (User/RS-232 Received Data Input) 3   Serial Port Interrupt 1   Timer B Interrupt 0   Timer A Interrupt
DD0E	CIA Control Register A 7   Time-of-Day Clock Frequency: 1 = 50 Hz, 0 = 60 Hz 6   Serial Port I/O Mode Output, 0 = Input 5   Timer A Counts: 1 = CNT Signals, 0 = System 02 Clock 4   Force Load Timer A: 1 = Yes 3   Timer A Run Mode: 1 = One-Shot, 0 = Continuous 2   Timer A Output Mode to PB6: 1 = Toggle, 0 = Pulse 1   Timer A Output on PB6: 1 = Yes, 0 = No 0   Start/Stop Timer A: 1 = Start, 0 = Stop
DD0F	CIA Control Register B 7   Set Alarm/TOD-Clock: 1 = Alarm, 0 = Clock 6-5 Timer B Mode Select:         00 = Count System 02 Clock Pulses         01 = Count Positive CNT Transitions         10 = Count Timer A Underflow Pulses         11 = Count Timer A Underflows While CNT Positive 4-0 Same as CIA Control Reg. A - for Timer B

 

Pin 1 GND – GrouND: Masse (0V) Pin 2-9 PA0-PA7   I/O   Parallel port a signals. Bidirectional parallel port. Pin 10-17 PB0-PB7   I/O Parallel port b signals. Bidirectional parallel port. Pin 18 PC O Handshake output. A low pulse is generated after a read or write on port b. Pin 19 TOD I Time od day clock input. Programmable 50hz or 60hz. Pin 20 Vcc – Supply voltage: +5V DC Pin 21 !IRQ O Interrupt output to microprocessor input IRQ. Pin 22 R/!W I READ/WRITE input Pin 23 !CS I Chip select input. A low pulse will activate CIA. Pin 24 !Flag I Negative edge sensitive interrupt input. Can be used as a handshake line for either parallel port. Pin 25 ø2 I clock input connected to processor Pin 26-33 DB0-DB7   I/O Bidirectional data bus. Connects to processor data bus. Pin 34 !RES I Low active reset input. Initializes CIA. Pin 35-38   RS0-RS3   I Register select inputs. Used to select all internal registers for communications with the parallel ports, time of day clock and serial port (SP). Pin 39 SP I/O Serial Port bidirectional connection. An internal shift register converts microprocessor parallel data into serial data, and vice versa. Pin 40 CNT I Count input. Internal timers can count pulses applied to this input. Can be used for frequency dependant operations.