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Working on README.
Also bring in Common at 0.8.0.
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‎.gitmodules‎

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[submodule "Neotron-Common-Hardware"]
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path = Neotron-Common-Hardware
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url = ../Neotron-Common-Hardware.git

‎Neotron-Common-Hardware‎

Submodule Neotron-Common-Hardware added at 674b6dc

‎README.md‎

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# Neotron-Pico
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# Neotron Pico
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> A Neotron system powered by the Raspberry Pi Pico, in a micro-ATX form-factor.
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The Neotron Pico is based around the idea of the [Neotron-32](https://github.com/neotron-compute/Neotron-32-Hardware), but using a low-cost Raspberry Pi Pico instead of a Texas Instuments Tiva-C Launchpad. It also stretches out to full micro-ATX size, and adds more expansion slots so that you can easily design and add your own peripherals.
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## Design
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The Raspberry Pi Pico is the core of the Neotron Pico. It uses PIO statemachines to generate 12-bit Super VGA video, and digital 16 bit 48 kHz stereo audio. It also has both I²C and SPI buses. SPI chipselects and IRQs are handled by an SPI-to-GPIO expander. This provides eight chip-selects and eight IRQs, to support up to eight expansion slots or peripherals. The eight chip-selects are gated with a tri-state bus transceiver, allowing the Pico to talk to either the I/O exander, or the selected expansion slot. The board has an SD fitted in the 'Slot 7' position, leaving Slot 0 through to Slot 6 available for expansion. Each expansion slot has I²C and SPI with unique chip-select and IRQ signals. A separate Board Mangement Controller also sits on the I²C bus handling PS/2 devices, and controlling power and reset. The BMC uses IRQ 7.
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## Software
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The Neotron Pico is designed to run the Neotron OS - a CP/M or MS-DOS alike OS written in Rust. But, being open-hardware, you can program your Neotron Pico to do pretty much anything.
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## Components
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### Processor
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The main processor module is the Raspberry Pi Pico, which features:
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* A Raspberry Pi Silicon RP2040 SoC
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* Dual-core Cortex-M0+ @ 133 MHz
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* 264 KiB internal SRAM
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* No internal Flash
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* USB 1.1
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* SPI, UART, I²C and _Programmable I/O_ peripherals
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* 26 GPIO pins
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* 2 MiB QSPI Flash
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* On-board LED
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* On-board 5V to 3.3V regulator
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* USB 2.0 Full-speed OTG micro-AB port
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* 4.00 USD / 3.60 GBP retail price
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The limited I/O on the Pico (we are using half the available pins just for the video output) is supplemented using a Microchip MCP23S17 SPI to GPIO expander, an octal buffer. The buffer allows the Pico to send its SPI bus data to either the MCP23S17 (to set a specific Chip Select line), or the rest of the system. Without the buffer, it would be impossible to command the MCP23S17 to disable a chip-select line once it had been set, without the traffic also going to the selected expansion slot!
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| Pin | Name | Signal | Function |
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| :--- | :--- | :------------- | :------------------------------------------------- |
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| xx | GPx | VGA_RED0 | Digital VGA signal, Red channel LSB |
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| xx | GPx | VGA_RED1 | Digital VGA signal, Red channel |
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| xx | GPx | VGA_RED2 | Digital VGA signal, Red channel |
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| xx | GPx | VGA_RED3 | Digital VGA signal, Red channel MSB |
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| xx | GPx | VGA_GREEN0 | Digital VGA signal, Green channel LSB |
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| xx | GPx | VGA_GREEN1 | Digital VGA signal, Green channel |
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| xx | GPx | VGA_GREEN2 | Digital VGA signal, Green channel |
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| xx | GPx | VGA_GREEN3 | Digital VGA signal, Green channel MSB |
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| xx | GPx | VGA_BLUE0 | Digital VGA signal, Blue channel LSB |
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| xx | GPx | VGA_BLUE1 | Digital VGA signal, Blue channel |
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| xx | GPx | VGA_BLUE2 | Digital VGA signal, Blue channel |
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| xx | GPx | VGA_BLUE3 | Digital VGA signal, Blue channel MSB |
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| xx | GPx | VGA_HSYNC | VGA Horizontal Sync (31.5 kHz) |
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| xx | GPx | VGA_VSYNC | VGA Vertical Sync (60 Hz) |
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| xx | GPx | I2C_SDA | I²C Data |
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| xx | GPx | I2C_SCL | I²C Clock |
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| xx | GPx | SPI_CLK | SPI Clock |
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| xx | GPx | SPI_CIPO | SPI Data In |
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| xx | GPx | SPI_COPI | SPI Data Out |
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| xx | GPx | SPI_CS_nIOCS | Low selects MCP23S17, High selects Expansion Slots |
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| xx | GPx | nIRQn | Interrupt Request Input from MCP23S17 |
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| xx | GPx | I2S_DAC_DATA | Digital Audio Output |
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| xx | GPx | I2S_ADC_DATA | Digital Audio Input |
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| xx | GPx | I2S_BIT_CLOCK | Digital Audio Bit Clock (1.536MHz) |
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| xx | GPx | I2S_LR_CLOCK | Digital Audio Sync (96kHz) |
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| xx | GPx | I2S_MAIN_CLOCK | Digital Audio Master Clock (12.288MHz) |
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### Super VGA output
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The Raspberry Pi Silicon RP2040 generates 12-bit VGA video at a range of standard resolutions (including 640x480 @ 60 Hz).
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* 15-pin D-Sub VGA interface
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* 12-bit (4-4-4) RGB R2R DAC
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* 3peak TPF133A or Texas Instruments THS7316 RGB video buffer
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* 36 MHz bandwidth - 1024x768@60Hz maximum
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* 6dB gain
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* Drives 75 ohm standard VGA interface
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* SOIC-8 package (1.27mm pitch)
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* Texas Instruments TPD7S019 Sync/DDC level shifter and RGB EMC filter
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* SSOP-16 package (0.635mm pitch)
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### Audio Codec
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The audio subsystem offers 16-bit 48 kHz stereo audio in and out through a classic blue/green/pink triple 3.5mm TRS jack. Input and Output volume can be software controlled.
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* Texas Instruments TLV320AIC23B
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* I²S + I²C interface
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* Amplified 32mW headphone output and line out
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* Microphone in and line in
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* TSSOP-28 package (0.635mm pitch)
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* Triple 3.5mm TRS jack (Kycon STX-4335-5BGP-S1)
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* Headphone Out (green)
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* Line In (blue)
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* Microphone In (pink)
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* AC'97 Pin Header for ATX cases with Audio Jacks
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* Headphone Out
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* Microphone In
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* Extra line-level output pin header (e.g. for additional RCA audio jacks - operates in addition to 3.5mm headphone jack output)
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* Internal line-level input pin header (e.g. for CD-ROM audio - disabled when 3.5mm line-in jack in-use)
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### Board Management Controller
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Power-on Reset sequencing, soft shutdown, voltage monitoring and PS/2 interfacing is handled by a separate STM32F0 SoC.
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* ST Micro STM32F0 (STM32F031K6T6) microcontroller
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* 32-bit Arm Cortex-M0+ Core
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* 3.3V I/O (5V tolerant)
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* 32 KiB Flash
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* 4 KiB SRAM
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* LQFP-32 package (0.8mm pitch)
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* Controls two PS/2 ports
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* Monitors 5V and 3.3V rails
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* Controls system reset, soft-on and soft-off for main CPU
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* Can the main 5V regulator on and off
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* Runs from 3.3V stand-by regulator
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* I²C interface (with dedicated IRQ line) with main CPU
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| Pin | Name | Signal | Function |
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| :--- | :--- | :------------ | :------------------------------------------------------ |
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| 14 | PB0 | - | Spare |
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| 15 | PB1 | - | Spare |
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| 26 | PB3 | - | Spare |
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| 27 | PB4 | PS2_CLK1 | Mouse Clock Input |
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| 28 | PB5 | PS2_DAT1 | Mouse Data Input |
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| 29 | PB6 | I2C_SCL | I²C Clock |
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| 30 | PB7 | I2C_SDA | I²C Data |
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| 2 | PF0 | - | Spare |
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| 3 | PF1 | - | Spare |
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| 6 | PA0 | MON_3V3 | 3.3V rail monitor Input (1.65V nominal) |
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| 7 | PA1 | MON_5V | 5.0V rail monitor Input (1.65V nominal) |
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| 8 | PA2 | UART_TX | UART Data Output |
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| 9 | PA3 | UART_RX | UART Data Input |
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| 10 | PA4 | /BUTTON_PWR | Power Button Input |
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| 11 | PA5 | STATUS_LED | Status LED Output |
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| 12 | PA6 | /BUTTON_RST | Reset Button Input |
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| 13 | PA7 | - | Spare |
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| 18 | PA8 | /IRQ | Interrupt Output |
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| 19 | PA9 | PS2_DAT0 | Keyboard Data Input |
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| 20 | PA10 | PS2_CLK0 | Keyboard Clock Input |
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| 21 | PA11 | /RESET | System Reset Output |
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| 22 | PA12 | DC_ON | PSU Enable Output |
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| 23 | PA13 | SWDIO | SWD Progamming Data Input |
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| 24 | PA14 | SWCLK_BOOT_TX | SWD Programming Clock Input OR Bootloader UART RX Input |
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| 25 | PA15 | BOOT_RX | Bootloader UART TX Output |
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### PS/2 Keyboard and Mouse
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* Kycon two-port stacked 6-pin DIN sockets (Kycon KMDGX-6S/6S-S4N)
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* Controlled via Board Management Controller
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### Power Supply
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* Unregulated 12V (8V to 28V) input fused with a PTC at 2A
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* 3A 5.0V main regulator (DC-DC switch-mode regulator module)
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* Morsun K7805-3AR3
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* 30mA 3.3V stand-by regulator (a micropower linear regulator)
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* 1A 3.3V regulator (a high-power 1117 type linear regulator)
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* Controlled by the Board Management Controller
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## Expansion
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The seven expansion sockets allow you to add on I²C or SPI based devices at a later date. Each provides a single chip-select and a single IRQ line - the motherboard design should ensure each socket gets a unique signal for each of these. Each expansion device should also contain a AT24C256 or similar EEPROM device. To allow these EEPROM devices to be scanned, each slot also contains three `EEPROM_ADDRESS` pins, tied to Vcc or GND in a unique combination. These should be connected through to the EEPROM address lines on your AT24C256, thus ensuring that each expansion card has its EEPROM at a unique address - 0x50 on Slot 0 through to a maximum possible 0x57 for Slot 7. Where your board has on-board devices, you should fit an AT24C256 EEPROM for each device so that the on-board devices can be discovered, exactly as if they were on an expansion card.
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The expansion slot is a simple 2x10 header. We suggest the use of a TE card-edge connector, but you could equally use two 1x10 pin-headers if desired.
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The pin functions are:
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```
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SPI_COPI 1 2 GND
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SPI_CIPO 3 4 GND
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SPI_CLK 5 6 GND
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~SPI_CS 7 8 ~IRQ
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I2C_SDA 9 10 I2C_SCL
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EEPROM_ADDR0 11 12 EEPROM_ADDR1
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EEPROM_ADDR2 13 14 ~RESET
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5V 15 16 5V
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3V3 17 18 3V3
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GND 19 20 GND
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```
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Four expansion slots line up with the ATX case expansion brackets, allowing you to use cards with external connectors. Three of the expansion slots are internal use only.
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## Expansion Ideas
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Why not design and build your own expansion card? You could try designing:
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* A dual Atari/SEGA 9-pin Joypad Interface
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* A Mikro Eletronika Click adaptor, allow many of the range of [Click board](https://www.mikroe.com/click) to be fitted
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* A Wi-Fi/Bluetooth card, using an Espressif ESP32
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* A second processor card - perhaps with a RISC-V microcontroller, or classic Zilog Z80
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* An OPL2 or OPL3 based FM synthesiser card
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* An ISA adaptor card (taking an ISA card at right-angles, i.e. parallel to the base board) - a simple microcontroller should be able to bit-bang the ISA bus at 8 MHz and offer an SPI peripheral interface to the Neotron Expansion Slot
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* An IDE interface card, allowing 40-pin IDE Hard Disk Drives and CD-ROM drives to be used - this will be quite similar to an ISA bus adaptor
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* A floppy drive controller card - either using an eSPI Super I/O chip, or connecting a legacy ISA bus floppy controller as per the ISA adaptor
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* A video card for a second monitor output, perhaps based on the CPLD used in the [VGAtonic](https://hackaday.io/project/6309-vga-graphics-over-spi-and-serial-vgatonic)
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## Changelog
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See [CHANGELOG.md](./CHANGELOG.md) for a list of detailed changes.
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## Licence
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These documents, schematics and PCB designs are Copyright (c) The Neotron Developers.
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[![CC BY-SA 4.0](https://i.creativecommons.org/l/by-sa/4.0/88x31.png)](http://creativecommons.org/licenses/by-sa/4.0/)
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This work is licensed under a [Creative Commons Attribution-ShareAlike 4.0 International License](http://creativecommons.org/licenses/by-sa/4.0/).
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## Contribution Agreement
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Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be licensed as above, without any additional terms or conditions.
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## Datasheets and References
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* Raspberry Pi Pico
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* Raspberry Pi Silicon RP2040
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* ST Microelectronics STM32F031K6T6
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* Morsun K7805-3AR3
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* Texas Instruments TLV320AIC23B
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* Texas Instruments THS7316
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* Texas Instruments TPD7S019

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