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Documentation : MCP23018

Pinouts and Pin assignments

+ indicates pin
o indicates unused pin
-s inserted between some of the pin functions for readability
OC** pins enclosed in parenthesis had lines over them in the pinout

MCP23018

                     Vss(GND) +01---.---28+ NC
                           NC +02       27+ GPA7
                         GPB0 +03       26+ GPA6
                         GPB1 +04       25+ GPA5
                         GPB2 +05       24+ GPA4
                         GPB3 +06       23+ GPA3
                         GPB4 +07       22+ GPA2
                         GPB5 +08       21+ GPA1
                         GPB6 +09       20+ GPA0
                         GPB7 +10       19+ INTA
                     Vdd(Vcc) +11       18+ INTB
                          SCL +12       17+ NC
                          SDA +13       16+ RESET
                           NC +14-------15+ ADDR

MCP32018 Pin Assignments

     power_negative  Vss(GND) +01---.---28o
                              o02       27o
            column0      GPB0 +03       26o
            column1      GPB1 +04       25+ GPA5   rowB
            column2      GPB2 +05       24+ GPA4   rowA
            column3      GPB3 +06       23+ GPA3   row9
            column4      GPB4 +07       22+ GPA2   row8
            column5      GPB5 +08       21+ GPA1   row7
            column6      GPB6 +09       20+ GPA0   row6
                              o10       19o
     power_positive  Vdd(Vcc) +11       18o
                I2C       SCL +12       17o
                I2C       SDA +13       16+ RESET  (see note)
                              o14-------15+ ADDR   (see note)

notes:
- ADDR (pin15): Set slave address to 0b0100000 by connecting to Vss(GND). (The user-defined bits are the three least significant).
- RESET (pin16) must be externally biased.Since we're not going to trigger it ourselves, we'll tie it high.
  - This is not noted in the I2C Pinout Description section of the MCP23018 datasheet, but it's true (empirically), and it is noted in the SPI Pinout Description section, and in the MCP23017 datasheet.
  - http://davidn.org/wp/?p=89
  - http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1293498979

Notes about Registers

register  address  function (for all bits)
--------  -------  -----------------------
IODIRA    0x00     \ 1: set corresponding pin as input
IODIRB    0x01     / 0: set ................. as output
GPPUA     0x0C     \ 1: set corresponding pin internal pull-up on
GPPUB     0x0D     / 0: set .......................... pull-up off
GPIOA     0x12     \ read: returns the value on the port
GPIOB     0x13     / write: modifies the OLAT register
OLATA     0x14     \ read: returns the value of this register
OLATB     0x15     / write: modifies the output latches that control the
                            pins configured as output

IOCON (see datasheet section 1.6, table 1-5, register 1-8)
- BANK: bit 7; read/write; default = 0
  - 1: The registers associated with each port are separated into different banks
  - 0: The registers are in the same bank (addresses are sequential)
- SEQOP: bit 5; read/write; default = 0
  - 1: Sequential operation disabled, address pointer does not increment
  - 0: Sequential operation enabled, address pointer increments
notes:
- All addresses given for IOCON.BANK = 0, since that's the default value of the bit, and that's what we'll be using.
- Outputs are open drain, so we want pull-up resistors set for everything.
- We want the row pins set as output high initially, and the column pins set as input. We'll cycle through driving the row pins low and checking the column pins in the update function.
abbreviations:
- IODIR = I/O Direction Register
- IOCON = I/O Control Register
- GPPU = GPIO Pull-Up Resistor Register
- GPIO = General Purpose I/O Port Register
- OLAT = Output Latch Register

I²C Device Protocol (see datasheet section 1.3, figure 1-1)

S  : Start       OP   : Device opcode
SR : Restart     ADDR : Device address
P  : Stop        Dout : Data out from MCP23018
W  : Write       Din  : Data in to MCP23018
R  : Read


S OP W ADDR ----> Din ... Din --> P
             |
             |--> SR OP R Dout ... Dout ---> P
             |<--------------------------|
             |
             |--> SR OP W ADDR ... Din --> P
             |
             |--> P

S OP R ----> Dout ... Dout --> P
        |
        |--> SR OP R Dout ... Dout ---> P
        |<--------------------------|
        |
        |--> SR OP W ADDR Din ... Din --> P
        |
        |--> P

Byte and Sequential Write
-------------------------
        Byte : S OP W ADDR --> Din --> P
  Sequential : S OP W ADDR --> Din ... Din --> P

Byte and Sequential Read
------------------------
        Byte : S OP W ADDR --> SR OP R Dout --> P
  Sequential : S OP W ADDR --> SR OP R Dout ... Dout --> P

notes:
- We'll be using sequential mode (ICON.SEQOP = 0; default) (see datasheet section 1.3.1).

5.5 KiB Raw Blame History

Documentation : MCP23018

Pinouts and Pin assignments

MCP23018

MCP32018 Pin Assignments

Notes about Registers

I²C Device Protocol (see datasheet section 1.3, figure 1-1)

5.5 KiB

Raw Blame History