PiPicoMite01

Features

Raspberry Pi Pico
- All Pico pins brought to headers
- Pin marking on rear
VGA
- 640x480, 320x240 resolutions
- 1:2:1 - R:G:B - 16 colors
PS/2 Keyboard
- 5V to keyboard with voltage translator
- Does not require a keyboard that runs at 3.3V
SD Card
- Full size card
- Up to 32GB
- FAT32 format
Stereo audio
- 3.5mm jack
16-bit GPIO
- MCP23017 port expander
- I2C1
- 2x10 0.1" pitch header
- Jumper selectable terminators
I2C0 connector (Rev 2 and later)
Power options
- 5V power input via USB Micro on Pico card, USB B, or 0.1" pitch header
- 3.3V output header
120mmx70mm outline
(4) 6-32 Mounting holes

BASIC Interpreter

The PicoMiteVGA boots straight into the MMBasic prompt. At which point you can enter, edit and save the program, test BASIC commands and run the program.

MMBasic is a Microsoft BASIC compatible implementation of the BASIC language. It is full featured with floating point, 64-bit integers and string variables, long variable names, arrays of floats, integers or strings with multiple dimensions, extensive string handling and user defined subroutines and functions. Typically it will execute a program up to 100,000 lines per second. Embedded compiled C programs can be used for even higher performance.

Using MMBasic you can use communications protocols such as I2C or SPI to get data from a variety of sensors. You can save data to an SD card, measure voltages, detect digital inputs and drive output pins to turn on lights, relays, etc.

The emphasis with MMBasic is on ease of use and development. The development cycle is very fast with the ability to instantly switch from edit to run. Errors are listed in plain English and when an error does occur a single keystroke will invoke the built in editor with the cursor positioned on the line that caused the error.

Pinout

Pin Marking on Rear

Schematic

Rev 1 Connectors

PicoMite01 Rev 1 Connectors - Note the Rev 1 connectors are in different sequence orders than the Rev 2 and later cards

Rev 2 Connectors

The following are for Rev 2 and later boards

J1 - MCP23017 - 16-bit GPIO

2x10 header
Includes power, ground

SetPin GP14, GP15, I2C2
I2C2 OPEN 400, 100
I2C2 WRITE &H20, 0, 2, &H00, &H00
I2C2 WRITE &H20, 0, 2, &H01, &H00
I2C2 WRITE &H21, 0, 2, &H00, &H00
I2C2 WRITE &H21, 0, 2, &H01, &H00

J2 - VGA

The VGA output is 640 x 480 pixels in monochrome mode or 320 x 240 pixels in colour mode with 16 colours (1 bit for red, 2 bits for green and 1 bit for blue). The VGA output is generated using the second CPU on the RP2040 processor plus one PIO channel so it does not affect the BASIC interpreter which runs at full speed on the first CPU. A handfull of components (resistors and a couple of diodes) is all that is required to connect the VGA monitor.

From within your BASIC program you can turn pixels on/off and draw lines, boxes and circles in any colour. Text can be positioned anywhere on the screen and displayed in any colour in a variety of fonts.

The built-in editor within MMBasic works perfectly with the VGA monitor and PS2 keyboard to allow programs to be edited (with colour coded text) and saved to an SD card.

J3 - 3.3V Power Out

J4 - Audio

Low Pass filter
Resistive voltage divider to get to line level
- Line Level Audio information
Two Tone Test
Play a WAV file

OPTION AUDIO GP6, GP7
PLAY WAV "file.wav"
PLAY STOP

J5 - USB B Power Connector

In parallel with J6

Full size USB B connector
No USB signal connections, just used for power

J6 - 5V Input

Useful to power the card from external 5V
Use in place of J5

J7 - PS/2 Keyboard

The PS2 keyboard connects to the Raspberry Pi Pico via a level shifter and works as a normal keyboard with the function keys and arrow keys fully operational. It can be configured for the standard US layout used in the USA, Australia and New Zealand or specialised layouts used in the United Kingdom, Germany, France and Spain.

5V keyboard

J8 - I2C0, UART0 (RTC, etc.)

I2C0SCL. UART0_TX (GP1)
I2C0SDA. UART0_RX (GP0)
VCC
GND

Can use Real Time Clocks using the PCF8563, DS1307, DS3231 or DS3232 chips means that the time is always accurately known.

J9,J10 Pico Connectors

Pico pins are brought out to 1x20 pin headers J9, J10

Pico Function Mapping

GP	FUNCTION	PICO PIN	GP	FUNCTION	PICO PIN
GP0	I2C1_INT (MCP23017)	1	GP16	VGA_HSYNC	21
GND	AUDIO-GND	8	GP17	VGA_VSYNC	22
GP6	AUDIO-L	9	GP18	VGA_BLU	24
GP7	AUDIO-R	10	GP19	VGA_GRN_LO	25
GP8	PS2_CLK	11	GP20	VGA_GRN_HI	26
GP9	PS2_DATA	12	GP21	VGA_RED	27
GP10	SD_SCK	14	VSYS	PS2_5V	39
GP11	SD_MOSI	15	3.3V	PS2_3.3V
GP12	SD_MISO	16	3.3V	SD_3.3V
GP13	SD_SLVSEL	17
GP14	I2C1_SDA (MCP23017)	19
GP15	I2C1_SCL (MCP23017)	20

SD1 - SD Card

The PicoMiteVGA firmware reserves eight program storage "slots" in the Raspberry Pi Pico flash memory. Programs can be saved and retreived from these without the need for any additional storage.

For more storage SD cards can be connected with full support for these built into MMBasic including the ability to open files for reading, writing or random access and loading and saving programs. SD cards connect directly to the Raspberry Pi Pico and the firmware will work with cards up to 32GB formatted in FAT16 or FAT32. The files created can be read and written on personal computers running Windows, Linux or the Mac operating system.

OPTION SDCARD GP13, GP10, GP11, GP12

H1 - I2C Terminators

2.2K terminators
Install shunts to terminate SDA, SCL signals that go to the on-board MCP23017 I2C Expander
Terminators are normally installed at the end of daisy-chained cards
I2C1 on Raspberry Pi Pico pins
I2C2 from MM BASIC
MM BASIC example commands

SETPIN GP14, GP15, I2C2
I2C2 OPEN 400, 100
I2C2 WRITE &H20, OC, LEN, B0[, B1...]
I2C2 READ &H20, OX, LEN, BUFF()

&H20 - I2C Address 0x20
OC: 0=terminate after, 1=chain next
len - Length of buffer (normally 1 for receive)
B0,B1... Bytes to send
BUFF() - receive buffer

H2 - MCP23017 - I2C Interrupt

Install shunt to connect INTA interrupt from MCP23017 to GP2 on Pico
MCP23017 interrupts can be set to generate interrupts on INTA pins for both A abd B ports
No Pull-up on card

Prototype Build

Raspberry Pi Pico MM BASIC Build
Built from Land Boards cards

Mechanicals

PicoMite Software

PicoMite Source code

PicoMite Source code
- Extra/replacement files for VGA

MCP23017 I2C Demo Code

PROTO16-I2C card
PIO16-01.BAS - GitHub repo
MCP23017 Datasheet
Set all 16 GPIO pins as outputs
Write alternate patterns, bounce a 1 across the outputs

SetPin GP14, GP15, I2C2
I2C2 OPEN 400, 100
I2C2 WRITE &H20, 0, 2, &H00, &H00
I2C2 WRITE &H20, 0, 2, &H01, &H00
I2C2 WRITE &H20, 0, 2, &H14, &H55
I2C2 WRITE &H20, 0, 2, &H15, &HAA
Pause 1000
I2C2 WRITE &H20, 0, 2, &H14, &HAA
I2C2 WRITE &H20, 0, 2, &H15, &H55
I2C2 CLOSE

MCP23008 Demo Code

I2CIO-8 card
MCP23008 Datasheet
I2CIO8-Bounce.bas - GitHub repo
- Bounce a bit across the 4 LEDs
I2CIO8-ReadWrite.bas - GitHub repo
Read 4 jumpers and write out LEDs

Tetris

> memory
Program:
  13K (10%) Program (485 lines)
  95K (90%) Free

RAM:
   8K ( 5%) 31 Variables
   0K ( 0%) General
 132K (95%) Free

Issues

Rev 2

Re-sequenced jacks and capacitors reference designators to left-to-right/top-to-bottom order
- In sequential order for easier assembly
Fixed MCP23017 I2C SDA/SCL pins
Added I2C Interface Header
Moved Vcc to the end of the GPIO connector

Rev 1

Tested and working
- Pico boots and runs
- VGA passes Colours.bas test
- PS/2 can type
- SD Card loads files
- Audio plays wav files

Issue with I2C connections to MCP23017 - Rework

SDA, SCL swapped to MCP23017
Cut etch solder side Pico pin 19 (to U2-12)
Cut etch solder side Pico pin 20 (to U2-13)
Cuts are done on rear side (CAD)
Verify cuts with ohmmeter

Cuts shown on board (using sharp Xacto knife)

Jumpers
Add wire Pico pin 19 to U2-13 (GP14)
Add wire Pico pin 20 to U2-12 (GP15)