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Documentation : MCP23018

Pinout and Pin assignments

+ indicates connected pin
o indicates unconnected pin
= is used to list other things the pin is connected to
-s inserted between some of the pin functions for readability

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

MCP23018 Pin Assignments

     power_negative  Vss(GND) +01---.---28o NC
                           NC o02       27o GPA7
              row_5      GPB0 +03       26+ GPA6   column_6
              row_4      GPB1 +04       25+ GPA5   column_5
              row_3      GPB2 +05       24+ GPA4   column_4
              row_2      GPB3 +06       23+ GPA3   column_3
              row_1      GPB4 +07       22+ GPA2   column_2
              row_0      GPB5 +08       21+ GPA1   column_1
                         GPB6 o09       20+ GPA0   column_0
                         GPB7 o10       19o INTA
     power_positive  Vdd(Vcc) +11       18o INTB
                I2C       SCL +12       17o NC
                I2C       SDA +13       16+ RESET  = Vdd(Vcc) (see note)
                           NC o14-------15+ ADDR   = Vss(GND) (see note)

notes:
- Row and column assignments are to matrix positions, which may or may or may not correspond to the physical position of the key: e.g. the key where row_4 and column_2 cross will be scanned into the matrix at [4][2], wherever it happens to be located on the keyboard. Mapping from one to the other (which only matters for defining layouts) is handled elsewhere.
- ADDR (pin15): Set slave address to 0b0100000 by connecting to Vss(GND).
  - The user-defined bits are the three least significant
  - I2C addresses are 7 bits long (the last bit in the byte is used for indicating read/write)
- RESET (pin16) must be externally biased. Since we're not going to trigger it ourselves, we can 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.
  - I'm not the first person who's failed to notice ;)
    - 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 register (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.
- Initially, we want either columns or rows (see <../options.h>) set as hi-Z without pull-ups, and the other set of pins set as input with pull-ups. During the update function, we'll cycle through setting the first set low and checking each pin in the second set.
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).

6.2 KiB Raw Blame History

Documentation : MCP23018

Pinout and Pin assignments

MCP23018

MCP23018 Pin Assignments

Notes about Registers

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

6.2 KiB

Raw Blame History