Front Panel For 8 Bit Computers

Front Panel for 8-Bit Microprocessors

• See here for V2 (through-hole) version

Top row controls

Typical controls.

Features

It has these features. They may not fit your generic design. Especially since this card has to have an I2C interface.

• 32 Pushbutton Switches
• 32 LEDs
• I2C interface (Two Wire interface - plus power and ground)
  • Jumper selectable base address
  • Occupies I2C addresses either 0x20-0x23 or 0x24-0x27
  • Jumper Selectable I2C terminators
• I2C daisy-chain connector
  • Interrupt line
    • Can be configured to interrupt on button presses
    • MCP23017 need to be set to Open-Drain output - card has pull-up to Vcc
• 4 MCP23017 16-bit I2C Port Expanders
  • These are fine pitch surface mount parts
  • MCP23017 Datasheet - Rev D
  • MCP23017... LOST TWO INPUTS
    • MCP23017 now a 14/16-bit expander, with two of the pins (GPA7 and GPB7) losing their input capabilities
    • The chips look the same, are called the same, and act mostly the same — if you don’t download the latest version of the datasheet (Revision D), you’d never know that there’s been a change
• 3.3V or 5V operation
• Compatible form factor with RETRO-EP4CE15 and other cards
  • 95x95mm
  • 6-32 mounting holes

Connector

J2 - I2C Connector

• Two row header on bottom of card
• 5 pin in
• 4 pin out (daisy-chain)

1. GND
2. VCC
3. SDA
4. SCL
5. INT*

And

1. GND
2. VCC
3. SDA
4. SCL

Schematic

• Front Panel Schematic Rev 1

Drivers

VHDL Driver

• VHDL code to control Front Panel autonomously
  • Great for FPGA Retro-computers
  • Converts pushbuttons into raw, debounced, and toggled outputs
  • Uses IOP16 small CPU core
  • Example: 6800 running MIKBUG using the Front Panel - Run/Halt the CPU, Read SRAM, ROM, etc, Write to SRAM

VHDL Entity

-- -------------------------------------------------------------------------------------------------------
-- Front Panel starts here
	
fp01 : work.FrontPanel01
  port map
  (
    -- Clock and reset
    i_CLOCK_50		=> i_CLOCK_50,		-- Clock (50 MHz)
    i_n_reset		=> w_resetClean_n,	-- Reset
    -- 32 outs, 32 ins
    i_FPLEDs		=> w_LEDsOut,		-- Out to LEDs (32)
    o_PBRaw		=> w_PBsRaw,		-- Raw version of the Pushbuttons (32)
    o_PBLatched		=> w_PBLatched,		-- Latched version of the Pushbuttons (32)
    o_PBToggled		=> w_PBsToggled,	-- Toggle version of the Pushbuttons (32)
    -- I2C interface
    io_I2C_SCL		=> io_I2C_SCL,		-- I2C clock to Front Panel card
    io_I2C_SDA		=> io_I2C_SDA,		-- I2C data to/from Front Panel card
    i_I2C_INTn		=> i_I2C_INTn		-- Interrupt input - active low
  );

-- Front Panel ends here
-- -------------------------------------------------------------------------------------------------------

Arduino Driver

• I2C parts are standard MCP23017 drivers which are supported in Arduino and most microprocessors
  • LandBoards_MCP23017 library
  • Importing an Arduino ZIP library

Micro-Python

• Micro-Python driver for MCP23017

C Code

• PSoC driver GitHub Repo
  • FrontPanel.c
  • FrontPanel.h
  • MCP23017.c
  • MCP23017.h

Assembly Sheet

Front Panel Assembly Sheet Rev 1