The goal of this project was to build a minimally complex Z80 computer capable of running CP/M. While I haven not yet ported CP/M, it should be capable of it.
This system is made of two boards, the upper board has the the CPU, RAM, ROM and UART. The lower board has Composite Video, USB Keyboard, USB to serial converter, Compact Flash and 8 indicator LEDs.
If you want to have a better understanding of how this system works you checkout the schematics or my blog.
- 64K Static RAM
- 32K ROM
- Z80 @ 4Mhz
- USB Keyboard via Raspberry Pi Zero
- Composite Video via Raspberry Pi Zero
- HDMI Video via Raspberry Pi Zero
- Support for 27256 or AT28C256 ROM
- Compact Flash
- 8 LED indicators
- Built-in USB to serial converter @ 9600 baud
As part of the project I wanted to have a composite video output however, there was not sufficient space to have a native composite video interface. As an alternative I have used a Raspberry Pi Zero running pigfx which acts as a terminal emulator providing a USB keyboard input and composite video output.
To the underside of the PCB solder in the Raspberry Pi using the pins from a 2.54mm header so that the Pi is flat against the PCB. Only the circles and yellow need to be soldered. Back on the top side of the PCB you will see some pads that need to be connected to some test points on the Pi, connect them using some wire cuts offs.
This system supports the W27C257, 27256 and AT28C256 ROM chips. The W27C257 and 27256 are read-only and need to have jumpers set in the topmost position. The AT28C256 is read/write and needs two jumpers in the lower position.
My assembler of choice for this project has been the Retro Assembler by Peter Tihanyi. There is a VSCode plugin available.
The early version of the monitor includes a utility "sboot" that will fetch data over the UART and store it in the lower 32k and jump to the start of memory.
For the serial bootloader to work you must be running the server utility that will provide the files for sboot to load. You can find it in software/server.
The sboot command can be configured to auto start on boot by setting UART_AUTO_BOOT to True in monitor.z80.asm and re-building.
This system has 64K of RAM and 32K of ROM. However, the Z80 can only ever address 64K at a time. When the system starts up the top 32K of memory maps to RAM, and the lower 32K maps to ROM. The system can, when ready, swap the lower 32K of ROM for RAM.
| Address | Device | R/W | Description |
|---|---|---|---|
| 0x10 | SIO | R/W | UART A Data Register |
| 0x11 | SIO | R | UART A Status Register |
| 0x12 | SIO | R/W | UART B Data Register |
| 0x13 | SIO | R | UART B Status Register |
| 0x20 | 8-bit Latch | W | LED Output |
| 0x30-37 | Compact Flash | R/W | Compact Flash Registers |
| 0x70 | Flip-flop | W | RAM/ROM Page |
Z80 Main Board Schematics - PDF
Compact Flash & Raspberry Pi Board - PDF
| Id | Designator | Footprint | Quantity | Designation | Supplier and ref | ||
|---|---|---|---|---|---|---|---|
| 1 | J2 | PinHeader_1x04_P2.54mm_Vertical | 1 | Conn_01x04_Male | |||
| 2 | C3,C2,C4,C5,C17,C12,C14,C6,C7,C16,C9,C13,C8,C10,C11,C15 | C_Disc_D3.0mm_W1.6mm_P2.50mm | 16 | 0.1uf | https://www.digikey.co.nz/en/products/detail/kemet/C320C104K5R5TA7303/3726160 | ||
| 3 | R2,R1,R3,R4 | R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | 4 | 2k7 | |||
| 4 | R5 | R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | 1 | 1k | |||
| 5 | C1 | C_Disc_D3.0mm_W1.6mm_P2.50mm | 1 | 150pF | https://www.digikey.co.nz/en/products/detail/vishay-beyschlag-draloric-bc-components/K151J15C0GF5TL2/286469 | ||
| 6 | U1 | DIP-40_W15.24mm_Socket | 1 | Z80CPU | |||
| 7 | U7 | DIP-40_W15.24mm | 1 | Z8440 | |||
| 8 | U14, U2 | DIP-28_W15.24mm | 1 | KM62256CLP | |||
| 9 | U13 | DIP-20_W7.62mm_Socket | 1 | 74LS374 | |||
| 10 | U5 | DIP-14_W7.62mm_Socket | 1 | 74LS04 | |||
| 11 | U9 | DIP-16_W7.62mm_Socket | 1 | 74LS161 | |||
| 12 | U3 | DIP_Socket-28_W11.9_W12.7_W15.24_W17.78_W18.5_3M_228-1277-00-0602J | 1 | 27256 | |||
| 13 | X1 | Oscillator_DIP-8 | 1 | CXO_DIP8 | https://www.digikey.co.nz/en/products/detail/abracon-llc/ACH-8-000MHZ-EK/675379 | ||
| 14 | U15 | TO-92 | 1 | DS1233 | https://www.digikey.co.nz/en/products/detail/analog-devices-inc-maxim-integrated/DS1233-5-T-R/1017808 | ||
| 15 | D2 | LED_D3.0mm | 1 | LED | |||
| 16 | U11,U8 | DIP-14_W7.62mm_Socket | 2 | 74LS74 | |||
| 17 | SW2 | SW_THT_SK-12F17-G_7-0 | 1 | SW_SPDT | https://www.digikey.co.nz/en/products/detail/c-k/SK-12F17-G-7/2747163 | ||
| 18 | U4 | DIP-14_W7.62mm_Socket | 1 | 74LS00 | |||
| 19 | SW1 | SW_PUSH_6mm_H4.3mm | 1 | SW_Push | https://www.digikey.co.nz/en/products/detail/cui-devices/TS02-66-70-BK-160-LCR-D/15634243 | ||
| 20 | U6 | DIP-16_W7.62mm_Socket | 1 | 74LS138 | |||
| 21 | J1 | PinSocket_2x16_P2.54mm_Vertical | 1 | Conn_01x32_Pin | |||
| 22 | J4 | BarrelJack_CUI_PJ-037A | 1 | Jack-DC | https://www.digikey.co.nz/en/products/detail/cui-devices/PJ-037A/1644545 | ||
| 23 | U12 | DIP-14_W7.62mm_Socket | 1 | 74LS32 | |||
| 24 | J7 | PinSocket_2x06_P2.54mm_Vertical | 1 | Conn_01x12_Male | |||
| 25 | J3 | PinHeader_2x03_P2.54mm_Vertical | 1 | Conn_02x03_Odd_Even |
| Id | Designator | Footprint | Quantity | Designation | Supplier and ref | ||
|---|---|---|---|---|---|---|---|
| 1 | R2 | R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | 1 | 100R | |||
| 2 | J2 | PinHeader_2x06_P2.54mm_Vertical | 1 | Conn_01x12_Male | |||
| 3 | J7,J8 | SolderWirePad_1x01_SMD_1x2mm | 2 | Conn_01x01_Pin | |||
| 4 | R8,R9,R7,R10 | R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | 4 | 10k | |||
| 5 | J5 | SWITCHCRAFT_PJRAN1X1U04X | 1 | RCA_Video | https://www.digikey.co.nz/en/products/detail/switchcraft-inc/PJRAN1X1U04X/969899 | ||
| 6 | U1 | CF-Card_101D-TAAB-R01 | 1 | Compact_Flash | https://www.digikey.co.nz/en/products/detail/attend-technology/101D-TAAB-R01/17633884 | ||
| 7 | U2 | DIP-20_W7.62mm | 1 | 74LS541 | |||
| 8 | Q2,Q1 | TO-92_Inline | 2 | 2N7000 | https://www.digikey.co.nz/en/products/detail/diotec-semiconductor/2N7000/13164314 | ||
| 9 | D2,D8,D6,D1,D4,D7,D5,D9,D3 | LED_D3.0mm_Horizontal_O1.27mm_Z2.0mm | 9 | LED | |||
| 10 | R1,R5,R6,R3,R4 | R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | 5 | 1K | |||
| 11 | U3 | SOP-8_3.9x4.9mm_P1.27mm | 1 | CH340N | https://vi.aliexpress.com/item/1005004980156804.html | ||
| 12 | R19,R20 | R_0805_2012Metric | 2 | 1k | https://www.digikey.co.nz/en/products/detail/stackpole-electronics-inc/RNCP0805FTD1K00/2240229 | ||
| 13 | R14,R15,R18,R11,R13,R16,R17,R12 | R_Axial_DIN0204_L3.6mm_D1.6mm_P7.62mm_Horizontal | 8 | 1k | |||
| 14 | J1 | Raspberry_Pi_Zero_Socketed_THT_FaceDown_MountingHoles | 1 | Raspberry_Pi_Zero | |||
| 15 | J4 | PinSocket_2x16_P2.54mm_Vertical | 1 | Conn_01x32_Pin | |||
| 16 | J6 | USB_Mini-B_Wuerth_65100516121_Horizontal | 1 | USB_B_Micro | https://www.digikey.co.nz/en/products/detail/amphenol-cs-commercial-products/GMSB0532112YEU/13683104 | ||
| 17 | J3 | 629104190121 | 1 | USB_A | https://www.digikey.co.nz/en/products/detail/w%C3%BCrth-elektronik/629104190121/6644275 | ||
| 18 | J10 | PinSocket_1x04_P2.54mm_Vertical | 1 | Conn_01x04_Pin | |||
| 19 | C1 | C_Disc_D3.0mm_W1.6mm_P2.50mm | 1 | 100pF | |||
| 20 | C2 | C_0805_2012Metric | 1 | 100nF | https://www.digikey.co.nz/en/products/detail/samsung-electro-mechanics/CL21B104KBCNNNC/3886661 |