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Pokémon mini Hardware Documentation

The Pokémon mini is a hand held created by Nintendo R&D3 around 1999. It is based around the Epson S1C88 Core (then Timex/Seiko), and it derives most peripherals from this system.

The machine has a 4 KiB on-board OTP BIOS, 4 KiB of internal RAM (shared with the LCD Controller) and a 21-bit cartridge bus. The entire system is controlled by writing to 256 hardware registers, most of which are Open-Bus.

CPU

Little-endian 8-bit model 3 S1C88V20 (aka E0C88V20) clocked 4.00 MHz. This is a S1C88 family chip, potentially customized for Nintendo (as there is no public documentation for the V20).

It has both 8-bit and 16-bit register as well as 8-bit page registers for extended addressing.

External bus with 21 bits for address & 8 bits for data.

Memory

  • BIOS: 4096 bytes, read-only.
  • Hardware Registers: Used to control Pokémon mini system.
  • Internal RAM: 4096 bytes, read/write access. Note: some RAM space may be required by the LCD controller and the bottom is used for the stack.
  • Internal EEPROM: 8192 bytes, read/write access via the I2C interface, used to store game saves.
  • Cartridge ROM: Up to 2 MiB addressable (16 megabits). Official carts have 512 KiB mask ROM.

Video

96x64 monochrome LCD, 1 bit per pixel (bpp), running at around a 75±10 Hz refresh rate. Toggling pixels allows to add a 3rd color with half tone.

It contains an on-glass controller which communicates on registers $20FE and $20FF as well as its own timer discussed below in Timers.

LCD Controller

The rate at which the image is redrawn and copied to the LCD (and which stages of rendering are enabled) is configurable.

  • Tiled backgrounds: 8x8 tiles, 4 different map sizes which expand beyond the screen boundaries, and a moveable display area (which does not loop automatically). The entire tilemap can be color inverted.
  • Sprites: 16x16 1 bpp with alpha mask, up to 24 sprites can be displayed at one time. Sprites can be individually activated, flipped, mirrored, and color inverted.

Sound

Single-channel square-wave with adjustable pulse-width played through a piezo speaker.

3 levels of volume: 0%, 50%, 100%. Commercial games achieve 25% and 75% by adjusting the pulse-width to achieve a weaker sound.

Can read back timer values (since sound is assigned to Timer 3).

For commercial games, hold the C button while booting up to start muted.

Timers

There are two oscillators and several timers/counters in the system. Additionally, the LCD has its own oscillator and timer, whose count value is exposed to the system.

OSC1 is 32768 Hz and is a low-power oscillator which cannot be disabled. OSC3 is 4.00 MHz and can be disabled by software. Entering sleep mode (but not halt mode) disables the oscillators.

  • 1x 24-bit seconds timer - increments each second, used for RTC, clocked by OSC1
  • 1x 8-bit 256Hz timer - increments each 1/256 of second, clocked by OSC1
  • 1x 8-bit counter provided by the LCD - counts 1 to 65 (inclusive)
  • 3x configurable timers, clocked by either OSC1 or OSC3 (configurable)
    • Each timer can operate as 1 16-bit counter or 2 8-bit counters.
    • Timer 3 is used for audio, but it can be used for more general purposes as well.

Extras

Power

1.5V (converted to 3.3V internally) with 1 AAA Battery