The Agon Light motherboard
Integrated Circuits
At the heart of the Agon Light are these three main ICs
- U1: EZ80F92 CPU
- U2: AS7C34096A SRAM (512Kb)
- U3: ESP32-PICO-D4 VDP (Visual Display Processor)
Interfaces
The main interfaces along the top of the board are fairly self-explanatory. The board is powered by the USB port.
There are additional GPIO pins along the bottom of the board with the following pinouts, looking down at the pins:
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 |
| GND | EZ80 PB3 SCK | EZ80 SDA . | EZ80 PB6 MISO | EZ80 PB2 CS | EZ80 PC6 . | EZ80 PC4 . | EZ80 PC2 . | EZ80 PC0 . | EZ80 PD6 . | EZ80 PD4 . | ESP I38 . | ESP IO26 . | ESP IO35 . | GND | GND |
| 3.3V | EZ80 PB7 MOSI | EZ80 SCL . | EZ80 CLK OUT | EZ80 PB5 . | EZ80 PC7 . | EZ80 PC5 . | EZ80 PC3 . | EZ80 PC1 . | EZ80 PD7 . | EZ80 PD5 . | ESP I37 . | ESP I39 . | ESP IO27 . | ESP I36 . | 5V |
| 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 |
All IO pins have zener diode protection to mitigate the risk of over-voltages from damaging the board.
Programming
The ESP32 can be programmed via the USB cable using the Arduino tools. Programming and debugging the EZ80 is done via the ZDI connector on the left-hand side of the board. This requires a Zilog USB Smart Cable (Part Number ZUSBSC00100ZACG).
More information on the toolchain can be found here.
Differences between Z80 and eZ80
The eZ80 is designed to be a low-power microcontroller for embedded devices and therefore includes hardware features more akin to an Arduino than a traditional Z80, including built-in UARTs, SPI and I²C interfaces, GPIO pins, a ZDI debugging interface, and DMA.
It is binary compatible with standard Z80, but can be switch between 8-bit and 24-bit mode either for blocks of code, or individual instructions. In 24-bit (ADL) mode, the CPU can address up to 16Mb of memory without paging, with support in the instruction set for 24-bit data. The chip has a 3-stage pipeline, and many instructions run with zero wait states. It is capable of running up to 3 times faster than an equivalent clocked Z80. There are also a handful of additional instructions to augment the standard Z80 set.