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:

12345678910111213141516
GNDEZ80
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
.
GNDGND
3.3VEZ80
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
17181920212223242526272829303132

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.