The aim of this project is to build a minimalistic computer with Z80 processor based on an Atmel AVR. That is the Z80 will run the code and the AVR will provide the rest like ROM, RAM and IO.
This is of course just a fun project with little practical sense.
- The hardware is wired on a breadbord.
- There is AVR code that provides ROM, RAM and access to the USART.
- The system has 6k Bytes of ROM and 384 Bytes of RAM.
- There is a really basic Z80 platform support library.
- The Z80 runs at 1/40 the speed of the AVR which is 200 kHz at 8 MHz.
- AVR interrupts can be forwarded to ISRs on the Z80.
- There is a Z80 example program written in C that can read and write strings via the USART.
- The Z80 example code has been extended to handle the timer interrupt.
__________________ (+) (+) (+) __________________
| | | | | | |
| ATmega8515 | | | | | Z80 CPU |
| | | | | | |
| VCC [40] |------+ | +---+------| [11] +5V |
| | 100n| 10k| 100n| | | |
| | _|_ / _|_ | | |
| | ___ \ ___ +------| [25] /BUSREQ |
| | | / | +------| [17] /NMI |
| | _|_ | _|_ +------| [24] /WAIT |
| | | | |
| PD3 [13] |----------------+----------------| [16] /INT |
| | | |
| PA0 [39] |---------------------------------| [30] A0 |
| PA1 [38] |---------------------------------| [31] A1 |
| PA2 [37] |---------------------------------| [32] A2 |
| PA3 [36] |---------------------------------| [33] A3 |
| PA4 [35] |---------------------------------| [34] A4 |
| PA5 [34] |---------------------------------| [35] A5 |
| PA6 [33] |---------------------------------| [36] A6 |
| PA7 [32] |---------------------------------| [37] A7 |
| | | |
| PE0 [31] |---------------------------------| [38] A8 |
| PE1 [30] |---------------------------------| [39] A9 |
| PE2 [29] |---------------------------------| [40] A10 |
| | | |
| PB2 [ 3] |---------------------------------| [ 1] A11 |
| PB3 [ 4] |---------------------------------| [ 2] A12 |
| | | |
| PC0 [21] |---------------------------------| [14] D0 |
| PC1 [22] |---------------------------------| [15] D1 |
| PC2 [23] |---------------------------------| [12] D2 |
| PC3 [24] |---------------------------------| [ 8] D3 |
| PC4 [25] |---------------------------------| [ 7] D4 |
| PC5 [26] |---------------------------------| [ 9] D5 |
| PC6 [27] |---------------------------------| [10] D6 |
| PC7 [28] |---------------------------------| [13] D7 |
| | | |
| PB0/OC0 [ 1] |---------------------------------| [ 6] CLK |
| | | |
| PD6 [16] |---------------------------------| [22] /WR |
| PD7 [17] |---------------------------------| [21] /RD |
| | | |
| PD4 [14] |---------------------+-----------| [26] /RESET |
| | LED | | |
| PB1 [ 2] |--------|>|-----+ | | |
| | LED | | | |
| PD5 [39] |----|>|----+ | | | |
| | | | | | |
| GND [20] |------+ | | | +------| [29] GND |
|__________________| | 1k5| 1k5| 10k| | |__________________|
| / / / |
| \ \ \ |
| / / / |
| | | | |
_|_ _|_ _|_ _|_ _|_
Note: Before commit addd1a97c2 the HALT pin has been connected to +5V by
mistake. This might cause a short circuit and must be avoided!
Note: I've changed the wiring a bit after commit 027f9489e4. One must not mix
older AVR code with the current wiring as there are conflicting output pins.
For simplicity I've left out the ISP port and the serial port.
I'm using a STK200 compatible parallel port programmer.
My current serial port implementation is build with an OPAmp and really needs improvement.
And that's how it looks like:
- GNU make
- AVR-GCC cross compiler
- SDCC
- SRecord
- AVRDUDE (UISP in older versions)
On a Fedora system simply type:
yum install make avr-gcc sdcc srecord avrdude
On my Fedora system the SDCC binaries are prefixed with sdcc-. You might need
to adjust this in the makefile if this isn't the case on your system.
Build the Z80 platform support library:
make -C z80lib
Build the Z80 native code example:
make -C z80code
Build the AVR part and link it with the Z80 ROM image:
make
Flash the AVR:
make isp
You might have to tweak the makefile for other programmers or AVR chips.
CPU User Manual: http://www.z80.info/zip/z80cpu_um.pdf
ATmega8515 datasheet: www.atmel.com/Images/doc2512.pdf
sdas manual: http://sdcc.svn.sourceforge.net/viewvc/sdcc/trunk/sdcc/sdas/doc/asxhtm.html