What is it?

My4TH light is the big brother of the My4TH XS computer board. In contrast to the My4TH XS it has an I2C interface that is 8 times faster than the I2C interface of the original My4TH board. This makes the I2C bus the ideal interface to connect all kinds of I/O, LCD and sensor breakout boards to this Forth computer. In addition, the My4TH light has a larger ROM than the My4TH XS, so that it has become possible to include a lot more additional functions in the firmware. For example, floating point words are now included in the ROM, so it is no more necessary to install them by loading an expansion module from the EEPROM. Also some software drivers for I2C based LCDs and also for general purpose I/O port expanders are now included. My4TH light has built-in support for:

HD44780 compatible LCDs using the PCF8574 chip for the I2C bus I/O port expander PCF8574, PCF8575, AW9523 and MCP23017 I2C-to-UART bridge SC16IS750 (provides a fast RS-232 interface with FIFO) Keyboard matrix up to 64x64 keys using a PCF8574 or PCF8575 This Forth-based computer board is an ideal platform for tinkering with a variety of breakout boards from Adafruit or other suppliers. Any board can be connected as long as it supports an I2C bus with 5V signal level. This includes all STEMMA boards and the newer Qwiic boards which have level shifters already on the board.

Why did you make it?

From http://mynor.org/my4th_xs.htm

What makes it special?

PCB size only 90 x 83 mm 13 logic ICs, 3 memory chips: 32 KB EPROM, 8 KB SRAM 64 KB EEPROM (optional) proven ALU-less design clock speed fixed at 8 MHz TTL-level UART with 4800 baud fast I2C bus with 83 kHz Forth 2012 operating system includes 295 standard words includes floating point support supports several I2C I/O chips