User Manual & Reference

Transcription

1 DreamCity Innovations M177v2 Reduced Human Interface Device User Manual & Reference Version 1C113 Applicable Devices: M177v2 M177v2-T M177v2-H M177v2-HT Applicable Firmware: M177v2 FW 1C114 Copyright 2015 Max Chan

2 TABLE OF CONTENTS TABLE OF CONTENTS 2 TABLES 3 1 OVERVIEW Variations 4 2 USING M177V Install the Hardware Install the Driver Library and Applications 5 3 THE M177V2 PROTOCOL The Operation of M177v M177v2 I2C Registers Overview The version Register (Register 0 Read) The reset Register (Register 0 Write) The i2c_addr Register (Register 1) The backlight Register (Register 2) The button Register (Register 3 read) The screen_ctrl Register (Register 3 Write) The protocol Register (Register 4 Read) The screen_cursor Register (Register 4 Write) The screen Register (Register 5 Write) The screen_char Register (Register 6 Write) The IRQ# Signal The RESET Signal 13 Page 2 of 13 Version 1C112

3 TABLES Table 1.1: M177v2 Variations Map 4 Table 3.1: Raspberry Pi GPIO Header 7 Table 3.2: M177v2 I2C Registers 8 Table 3.3: button register bitmap 10 Table 3.4: Commands multiplexed in screen_ctrl register 10 Table 3.5: screen_cursor Register Bitfield Description 12 Page 3 of 13 Version 1C112

4 1 OVERVIEW M177v2 is a reduced human interface device, providing a 16x2 character LCD and 4 physical buttons, for single-board computers that is compatible with Raspberry Pi Model A+, B+ and Raspberry Pi 2. M177v2 is powered by an Atmel ATmega328P microcontroller, acting as a intermediate between the host microprocessor and the human interface hardware, a Hitachi HD44780-compatible 16x2 LCD screen and four hardware buttons. M177v2 allows high-level access to the LCD using commands and provides software debounce and interrupts to the hardware buttons. M177v2 communicates with the host hardware using the I 2 C bus and two discrete signals: IRQ# and RESET. M177v2 pulls the IRQ# line low when a button action is detected and releases the line when button status is read. The host can hard reset M177v2 by asserting the RESET line high. The ATmega328P on M177v2 have 16MHz 32-pin Optiboot bootloader installed and is compatible with the Arduino environment. Pin mapping between M177v2 hardware and Arduino Mini Pro is listed in the firmware source code. 1.1 Variations For M177v2-T and M177v2-HT, a Maxim DS3231 DTCXO real-time clock is added to the PCB, allowing the host device to keep time precisely. For M177v2-H and M177v2-HT, an Atmel AT24C64 EEPROM chip is added to the PCB with appropriate information written to conform to the Raspberry Pi HAT specification. Table 1.1: M177v2 Variations Map No RTC DS3231 DTCXO RTC No HAT compatibility M177v2 M177v2-T HAT-compatible M177v2-H M177v2-HT Page 4 of 13 Version 1C112

5 2 USING M177V2 2.1 Install the Hardware M177v2 is shipped to you with the screen installed securely with copper spacers and screws, and the firmware is preinstalled. To install the module onto your Raspberry Pi : 1. Mount the long spacers loosely on the M177v2 module with the screws 2. Press the module onto the Raspberry Pi PCB firmly, making sure the mating connectors line up. 3. Screw the short spacers into the long spacers from the bottom of the Raspberry Pi PCB firmly. 4. Tighten the screws to fix the modules onto the Raspberry Pi. 2.2 Install the Driver Library and Applications You have to build the driver library, librhid, from source. You need to install the dependency libi2c-dev first. Then download the library from either by checking out from the version control directly, or by unpacking the downloaded tarball. There is no need to configure this package. Issue the make command to build, and if you are using Raspberry Pi 2, issue make -j4 to use all four cores to compile this project in parallel. Issue sudo make install to install the library and headers into the /usr/local directory. You can override this installation target, for example to the /usr directory, with sudo install prefix=/usr. Page 5 of 13 Version 1C112

6 Documentation of librhid is separate from this hardware user manual. You can read this manual at Page 6 of 13 Version 1C112

7 3 THE M177V2 PROTOCOL M177v2 communicates with the Raspberry Pi with four signals and uses all three available power rails on the GPIO header: Table 3.1: Raspberry Pi GPIO Header GPIO # Signal Name Direction Comments 2 SDA I 2 C I/O 3 SCL I 2 C Input I 2 C bus 4 IRQ# CMOS Open-drain This pin is pulled low when M177v2 detected button action. 22 RESET CMOS Input When this pin reads high, M177v2 is hard reset. +5V +5V Power 5V power rail for the main MCU and the screen. +3.3V +3.3V Power 3.3V power rail for the level shifters, RTC and EEPROM. GND GND Power Ground. Most of the communications happened on the I 2 C bus. By default, M177v2 uses the address 0x46, however this can be changed by writing the new, valid I 2 C address to the i2c_addr register and issue a reset to make it take effect. 3.1 The Operation of M177v2 When the M177v2 is powered on or released from reset, it displays its firmware version and I 2 C address on the screen for a second, and start waiting for commands from the I 2 C bus with words Initializing shown on screen and a dimmed backlight. Since firmware version 1C113, upon receiving the first I2C command the screen is cleared before During reset and the one-second splash screen M177v2 is not respond to any request on the I 2 C bus. This allows the user program to detect the I2C address of M177v2 by scanning devices twice, first time right after M177v2 is held in reset and second time after it is waiting for commands, and detect a failed software reset by scanning the Page 7 of 13 Version 1C112

8 bus 50 milliseconds and a few seconds after a software reset is issued, and reissue a hard reset should software reset fail. 3.2 M177v2 I 2 C Registers Overview For every command to M177v2 it always start with a one-byte write to select the register. A few read-only and write-only registers share addresses. After finishing a command, a new command can start immediately without restarting the transmission, although it is highly recommended to restart the transmission to prevent the M177v2 entering a confused state accidentally. After reading or writing a byte from a register, the register address is not advanced. Some registers allow reading or writing streams of multiple bytes (stream registers,) while others reads or writes one byte (byte registers.) Undefined register cannot be written, and always reads 0. Table 3.2: M177v2 I 2 C Registers Register # Reading Writing 0 version reset 1 i2c_addr 2 backlight 3 button screen_ctrl 4 protocol screen_cursor 5 N/A screen 6 N/A screen_char For those familiar with the Arduino platform, the registers and commands controlling the LCD screen corresponds to the LiquidCrystal class, as it is the underlying library supporting the screen on M177v2. Page 8 of 13 Version 1C112

9 3.3 The version Register (Register 0 Read) The version register is a read-only stream register. When read, it returns a nullterminated string with the current firmware version, for example M177v2 FW 1C113. The version register is available since firmware version 1A The reset Register (Register 0 Write) The reset register is a write-only byte register that triggers a software reset when written with value either 0x55 or 0xAA. Any other written value will be ignored. The reset register is available since firmware version 1A The i2c_addr Register (Register 1) The i2c_addr register is a read/write byte register containing the 7-bit I 2 C address of M177v2. Change to this register does not take effect until the next reset. This is useful when adding new devices on the I2C bus may cause address collisions. The i2c_addr register is available since firmware version 1A The backlight Register (Register 2) The backlight register is a read/write byte register containing the brightness of the backlight of the screen. Brightness of 0 means the backlight is off and brightness of 255 means the screen is full on. You can reduce the module and the entire system s energy consumption by reducing the screen s brightness. When set to a value different than current brightness, the backlight adjusts from its current state to the state set in the register in a fade. The backlight register is available as write-only register since firmware version 1A28 and became read/write in firmware version 1A105. Page 9 of 13 Version 1C112

10 3.7 The button Register (Register 3 read) The button register is a read-only byte register that returns the state change of the buttons when read as a bitmap. The bits are, from MSB to LSB: Table 3.3: button register bitmap Bit # MSB Meaning ESC button released 6 ESC button pressed 5 PREV button released 4 PREV button pressed 3 OK button released 2 OK button pressed 1 NEXT button released LSB NEXT button pressed If you did not read the button register before the button s state (pressed or released) is changed the previous state is lost. Due to this behaviour of the button register it is recommended to interrupt on the falling edge of IRQ# signal and upon the signal going low, read this register. Reading this register have the side effect of resetting its content to 0 and releasing the IRQ# signal. The button register is available since firmware version 1A The screen_ctrl Register (Register 3 Write) The screen_ctrl register is a write-only byte register that contained multiple LCD control commands multiplexed into one register. Table 3.4: Commands multiplexed in screen_ctrl register Page 10 of 13 Version 1C112

11 Cmd # Command name Comments 0 clear Clears the screen and places the cursor to the first character of the first line. 1 home Places the cursor to the first character of the first line. 2 cursor Show the static underscore cursor. 3 nocursor Hide the static underscore cursor. (default) 4 blink Show the blinking box cursor. 5 noblink Hide the blinking box cursor. (default) 6 display Show contents previously hidden. (default) 7 nodisplay Hide contents of the screen without clearing it. 8 scrolldisplayleft Scroll the entire display s contents left by one character. 9 scrolldisplayright Scroll the entire display s contents right by one character. 10 lefttoright Incoming text is added in left-to-right mode. (default) 11 righttoleft Incoming text is added in right-to-left mode. 12 autoscroll Enables automatic scrolling of text. 13 noautoscroll Disables automatic scrolling of text. (default) Changing the text directing (commands lefttoright and righttoleft) does not affect existing text. Anything else written to this register will be ignored. The screen_ctrl register is available since firmware version 1A The protocol Register (Register 4 Read) The protocol register is a read-only byte register containing the protocol version number. Currently it reads as 4. This register have little use now but will become a compatibility feature in the future. The protocol register is available since firmware version 1C112. Page 11 of 13 Version 1C112

12 3.10 The screen_cursor Register (Register 4 Write) The screen_cursor register is a write-only byte register that is used to move the cursor around the screen. The row and column numbers are fit into one byte in a bitfield style. Table 3.5: screen_cursor Register Bitfield Description Bit # MSB 6 Description Line number (0-3) Character number in the line (0-63) 1 LSB The screen_cursor register is available since firmware version 1A The screen Register (Register 5 Write) The screen register is a write-only stream register. Characters written to this register is sent to the screen, verbatim. The screen register is available since firmware 1A The screen_char Register (Register 6 Write) The screen_char register is a write-only fixed-length stream register. It takes 9 bytes on input. The lower 3 bits of the first byte is the character to define, and the lower 5 bits of the 8 bytes forms the bitmap of the character. Page 12 of 13 Version 1C112

13 After you have written to the screen_char register to define a character in the 0-7 range, a subsequent write to screen register with the corresponding code will cause the bitmap to be shown on the screen. The screen_char register is available since firmware 1A The IRQ# Signal The IRQ# signal is a LVCMOS open-drain output from M177v2. When in released state it is pulled up by a resistor, and when asserted it is pulled down by a CMOS open drain output. The IRQ# signal is asserted when there is unprocessed button events and is cleared when it is retrieved by reading the button register. Due to the fact that unprocessed button events can get overridden by new events from the same button, it is highly recommended to interrupt on the falling edge of the signal and retrieve button events as soon as possible The RESET Signal The RESET signal is a 3.3V LVCMOS input to M177v2 with internal pull-down. When the Raspberry Pi outputs a high level on this pin, M177v2 is held in reset until this pin is turned low again. Page 13 of 13 Version 1C112