148 lines
6.2 KiB
Markdown
148 lines
6.2 KiB
Markdown
# Documentation : MCP23018
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## Pinout and Pin assignments
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* `+` indicates connected pin
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* `o` indicates unconnected pin
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* `=` is used to list other things the pin is connected to
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* `-`s inserted between some of the pin functions for readability
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### MCP23018
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Vss(GND) +01---.---28+ NC
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NC +02 27+ GPA7
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GPB0 +03 26+ GPA6
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GPB1 +04 25+ GPA5
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GPB2 +05 24+ GPA4
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GPB3 +06 23+ GPA3
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GPB4 +07 22+ GPA2
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GPB5 +08 21+ GPA1
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GPB6 +09 20+ GPA0
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GPB7 +10 19+ INTA
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Vdd(Vcc) +11 18+ INTB
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SCL +12 17+ NC
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SDA +13 16+ RESET
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NC +14-------15+ ADDR
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### MCP23018 Pin Assignments
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power_negative Vss(GND) +01---.---28o NC
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NC o02 27o GPA7
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row_5 GPB0 +03 26+ GPA6 column_6
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row_4 GPB1 +04 25+ GPA5 column_5
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row_3 GPB2 +05 24+ GPA4 column_4
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row_2 GPB3 +06 23+ GPA3 column_3
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row_1 GPB4 +07 22+ GPA2 column_2
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row_0 GPB5 +08 21+ GPA1 column_1
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GPB6 o09 20+ GPA0 column_0
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GPB7 o10 19o INTA
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power_positive Vdd(Vcc) +11 18o INTB
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I2C SCL +12 17o NC
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I2C SDA +13 16+ RESET = Vdd(Vcc) (see note)
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NC o14-------15+ ADDR = Vss(GND) (see note)
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* notes:
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* Row and column assignments are to matrix positions, which may or may
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or may not correspond to the physical position of the key: e.g. the key
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where `row_4` and `column_2` cross will be scanned into the matrix at
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`[4][2]`, wherever it happens to be located on the keyboard. Mapping
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from one to the other (which only matters for defining layouts) is
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handled elsewhere.
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* ADDR (pin15): Set slave address to `0b0100000` by connecting to Vss(GND).
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* The user-defined bits are the three least significant
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* I2C addresses are 7 bits long (the last bit in the byte is used for
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indicating read/write)
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* RESET (pin16) must be externally biased. Since we're not going to
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trigger it ourselves, we can tie it high.
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* This is not noted in the I2C Pinout Description section of the
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MCP23018 datasheet, but it's true (empirically), and it is noted in
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the SPI Pinout Description section, and in the MCP23017 datasheet.
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* I'm not the first person who's failed to notice ;)
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* <http://davidn.org/wp/?p=89>
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* <http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1293498979>
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## Notes about Registers
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register address function (for all bits)
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-------- ------- -----------------------
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IODIRA 0x00 \ 1: set corresponding pin as input
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IODIRB 0x01 / 0: set ................. as output
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GPPUA 0x0C \ 1: set corresponding pin internal pull-up on
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GPPUB 0x0D / 0: set .......................... pull-up off
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GPIOA 0x12 \ read: returns the value on the port
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GPIOB 0x13 / write: modifies the OLAT register
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OLATA 0x14 \ read: returns the value of this register
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OLATB 0x15 / write: modifies the output latches that control the
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pins configured as output
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* IOCON register (see datasheet section 1.6, table 1-5, register 1-8)
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* BANK: bit 7; read/write; default = 0
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* 1: The registers associated with each port are separated into
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different banks
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* 0: The registers are in the same bank (addresses are sequential)
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* SEQOP: bit 5; read/write; default = 0
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* 1: Sequential operation disabled, address pointer does not increment
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* 0: Sequential operation enabled, address pointer increments
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* notes:
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* All addresses given for IOCON.BANK = 0, since that's the default value of
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the bit, and that's what we'll be using.
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* Initially, we want either columns or rows (see <../options.h>) set as
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hi-Z without pull-ups, and the other set of pins set as input with
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pull-ups. During the update function, we'll cycle through setting the
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first set low and checking each pin in the second set.
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* abbreviations:
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* IODIR = I/O Direction Register
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* IOCON = I/O Control Register
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* GPPU = GPIO Pull-Up Resistor Register
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* GPIO = General Purpose I/O Port Register
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* OLAT = Output Latch Register
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## I²C Device Protocol (see datasheet section 1.3, figure 1-1)
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S : Start OP : Device opcode
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SR : Restart ADDR : Device address
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P : Stop Dout : Data out from MCP23018
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W : Write Din : Data in to MCP23018
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R : Read
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S OP W ADDR ----> Din ... Din --> P
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|--> SR OP R Dout ... Dout ---> P
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|<--------------------------|
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|--> SR OP W ADDR ... Din --> P
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|--> P
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S OP R ----> Dout ... Dout --> P
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|--> SR OP R Dout ... Dout ---> P
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|<--------------------------|
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|--> SR OP W ADDR Din ... Din --> P
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|--> P
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Byte and Sequential Write
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-------------------------
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Byte : S OP W ADDR --> Din --> P
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Sequential : S OP W ADDR --> Din ... Din --> P
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Byte and Sequential Read
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------------------------
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Byte : S OP W ADDR --> SR OP R Dout --> P
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Sequential : S OP W ADDR --> SR OP R Dout ... Dout --> P
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* notes:
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* We'll be using sequential mode (ICON.SEQOP = 0; default) (see datasheet
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section 1.3.1).
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-------------------------------------------------------------------------------
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Copyright © 2012 Ben Blazak <benblazak.dev@gmail.com>
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Released under The MIT License (MIT) (see "license.md")
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Project located at <https://github.com/benblazak/ergodox-firmware>
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