TheYAZ180 is a modern single board computer, built on the tradition rich Z180 CPU and the AMD Am9511A-1 APU.
It is my attempt to create a perfect mix of"ancient"and modern computing technology. Specifically, it is an attempt to marry CPU/APU technology from 40 years ago, with modern I2C, USB, and WiFi capabilities, and make an powerful 8-bit computer that can either be embedded into an application, or operate as a stand-alone computer (with some accessories).
The YAZ180 is supported by the Z88dk and it is designed to work with both traditional CP/M v2.2 applications and modern Z88dk C compiled programs.
The YAZ180 is fully open source. All documentation and design is available from this repository. I will be making the raw PCBs and completed YAZ180 boards available on Tindie, shortly.
The Z180 CPU is based on the Z80 CPU, but it includes a number of integrated peripherals including a basic Memory Management Unit (MMU), two serial interfaces (ASCI0 & ASCI1), two DMA controllers (DMAC0 & DMAC1), and two Programmable Reload Timers (PRT0 & PRT1).
The fastest readily available Flash memory is 55ns. This is matched by the fastest RAM in 8 x 1MByte packaging at 45ns. Using these two timings the fastest clock that can be therefore be supported is approximately 20MHz. Using this as a guide, and knowing that the Z180 ASCI interfaces are happiest running at a magic frequency, I have therefore selected 18.432MHz as the basic operating frequency (or Phi) for the YAZ180.
The Z180 can operate internally at 2x the external Phi clock, which means that the YAZ180 is configured to run at 36.864MHz in normal situations. This is slightly outside the Z180 specification (33MHz), but this frequency is widely recommended even in Zilog documentation.
The AMD Am9511A (1977) was the first hardware arithmetic Floating Point Unit (FPU) developed. It is essentially a"scientific calculator"on a chip, and is capable of both 16 bit and 32 bit fixed and 32 bit floating point processing, across all the standard and trancendental functions. Even though this device is 40 years old, it is still comparable in performance of mathematical calculation to its Z180 host.
In addition to the internal Z180 interfaces, I have added a 82C55 Programmable Peripheral Interface (PPI) Controller (1974). This device provides 3x 8 bit parallel ports, and enables the YAZ180 to support 16bit IDE hard drives, as well as providing a mechanism to add parallel data interfacing to future expansion boards.
As the IDE interface requires control signals that are active low, several of the PPI Port C lines are passed through inverters. Importantly, those Port C lines that can accept input in PPI Mode 1 or Mode 2 are not inverted, and are therefore available as inputs from off-board applications. The IDE physical interface cable also provides a tidy board extension format, to allow extension or accessory devices to be attached to the YAZ180.
A single step circuitry has been implemented, which is enabled by a switch, and triggered by writing to an I/O port address. This enables the YAZ180 to run normally, until it becomes interesting to enable a breakpoint.
To interface with modern sensors and devices, two separate I2C interface PCA9665 devices have been provided. This enables one I2C device to be running at 1MHz in Fast-mode Plus (or even Turbo mode) driving a LCD controller for a screen (for example FTDI EVE), and have the other I2C interface connected over longer distances to sensors or keyboard running at 100kHz in Standard mode. The PCA9665 has deep 68 byte hardware buffers, and can operate in buffered or streaming mode, enabling complete I2C sentences to be transmitted or received without CPU interaction. A complete GL graphics command can be sent with one CPU DMA, for example.
To interface with TCP/IP networks, using WiFi, an ESP8266 pin-out for the ESP-01S is provided, connected to ASCI1. This enables the YAZ180 to operate as an Internet server (with attached IDE hard drive), and / or to be controlled using Secure Shell from anywhere.
A USB parallel interface is provided to enable"tool-less"programming of the YAZ180. A perl script is provided to upload Intel HEX code and program it into the system Flash memory. To enable this feature hardware is provided to reconfigure the memory map to allow boot from USB.
The YAZ180 PCB is 160mm x 100mm in size, with 4 layers.This is the maximum size supported by the Eagle"Hobby Licence", which was used to create the PCB.
