Front Panel for 8 Bit Computers V2

Front Panel for 8-Bit Microprocessors v2

See here for Ver 1 - SMT version

Features

This is a through-hole version of Front Panel for 8_Bit Computers.

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 of MCP23017 16-bit I2C Port Expanders
  • These are fine pitch surface mount parts
• 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

Legends

• D0-D7 - Data bus
• A0-A15 - Address bus
• Controls

Top row controls

Board has typical control silkscreen markings. It is all through hole so that it is much easier to assemble.

• RUN - Run/Halt pushbutton, RUN LED on for CPU running
• RESET - Reset the CPU
• STEP - Single Step the CPU
• Undefined
• CLEAR - Clear address bus (if SETADR is ON) or data bus lines (if SETDAT is ON)
• INCADR - Increment the address
  • If SETDAT is on write data
• SETDAT - Set the data value
• SETADR - Set the address

Drivers

VHDL Driver

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

VHDL Entity

-- -------------------------------------------------------------------------------------------------------
-- Front Panel starts here
-- Pass IOP16 code size and stack size down to the Front Panel
fp01 : work.FrontPanel01
	generic	map ( 
		INST_ROM_SIZE_IN	=> 512,			-- 512W code size
		STACK_DEPTH_IN		=> 4			-- 16 deep stack size
	)
	port map
	(
		-- Clock and reset
		i_CLOCK_50		=> i_CLOCK_50,		-- Clock (50 MHz)
		i_n_reset		=> i_n_reset,		-- Reset (from FGPGA KEY)
		-- 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
-- -------------------------------------------------------------------------------------------------------

6800 with Front Panel Operation

• Memory map for this configuration is

0x0000-0x7FFF - INTERNAL SRAM
0x8018-0x8019 - VDU (serSelect J3 JUMPER REMOCED)
0x8028-0x8019 - ACIA
0x8030-0x803F - Front Panel
0xC000-0xFFFF - MIKBUG ROM - Copied 4X

Halt CPU

• Card comes up running SMITHBUG at 0xC000
• RUN LED comes up on
• A0-A15 LEDs light "dimly" once CPU is running
• Other control LEDs off
• Press RUN SW32 to halt CPU, LED will go off
• A0-A31, D0-D7 LEDs may be off if run first time
  • May come up at address 0x0000 and show value in SRAM at that address (0x00 at power on)

Read from Program ROM

• Enter address set mode by pressing SW24 SETADR pushbutton, LED will illuminate
• Set address to 0xC000 by pressing A31, A30, LEDs will light
• Press SETADR pushbutton again to exit set address mode, LED will go off
• For MIKBUG, data will be 0x8E
• Press INCADR SW26
• Address will increment to 0xC001
• Data will show 0x7F
• Next INCADR values are as follows

   c000                 START EQU *
   c000   8e 7f 44      	LDS #STACK
   c003   bf 7f 0a      	STS SP
   c006   7f 7f 0d      	CLR ECHO
   c009   ce c1 25      	LDX #SFE
   c00c   ff 7f 17      	STX SWIPTR
   c00f   ff 7f 08      	STX NIO

Access SRAM

• Enter address set mode by pressing SW24 SETADR pushbutton, LED will illuminate
• Set address to 0x0000
• Press SETADR pushbutton again to exit set address mode, LED will go off
• Press INCADR pushbutton to read data
• Press SETDAT pushbutton to enter write data mode
• Set the data value to write to SRAM on pushbuttons
• Press INCADR to do the write and advance the address
• Press SETDAT pushbutton again to exit write data mode
• Verify data as above

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

PSoC Control

• Z80 example

C Code

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

Assembly Sheet

Front Panel V2 Assembly Sheet Rev 1