easy_z80
Publicskiselev/easy-z80
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Imported from GitHub: skiselev/easy_z80 · commit c236fe8 · license GPL-3.0
Description
An easy to build Zilog Z80 based single board computer
README
Easy Z80
An easy to build Zilog Z80 based single board computer
Table of Contents
Introduction
My son Max asked me what it takes to build a computer, and whether or not he can design and build one himself. This project is our attempt to design and build a simple, easy to understand, yet capable single board computer. It reuses the same memory paging mechanism I've implemented in Zeta SBC V2. It uses the Zilog Z80 SIO/O, Z80 CTC peripheral ICs, and implements daisy chain mode 2 interrupt configuration.
Specifications
- Processor: Zilog Z80 CPU (CMOS version - Z84C00)
- Memory: 512 KiB battery-backed SRAM, 512 KiB Flash ROM
- I/O:
- Zilog Z80 CTC - Programmable timer used for periodic interrupts and (optionally) for generating UART clock
- Zilog Z80 SIO - Dual channel serial interface, used for console and for connecting to other peripheral devices
- Bus: RC2014 compatible
- Microprocessor Supervisor:
- Reset generation
- SRAM battery backup
- Power failure NMI
- Watchdog (optional)
Hardware Documentation
For the version 1.0 schematic, PCB layout, and bill of materials please refer to tag v1.0
Schematic and PCB Layout
Connectors and Jumpers
J1 - Power
Connect regulated +5V power supply to this connector.
| Pin | Signal Name | Description |
|---|---|---|
| Tip (the inner contact) | VCC | Positive terminal - +5V |
| Barrel / sleeve | GND | Negative terminal - ground |
J2, J3 - Serial Channel A and Serial Channel B
| Pin | Signal Name | Description |
|---|---|---|
| 1 | DCD | Carrier Detect; Not used - Not connected on the SBC |
| 2 | RXA, RXB | Receive Data; Input to SBC |
| 3 | TXA, TXB | Transmit Data; Output from SBC |
| 4 | DTR | Data Terminal Ready; Not used - Not connected on the SBC |
| 5 | GND | Connected to the SBC GND signal |
| 6 | DSR | Data Set Ready; Not used - Not connected on the SBC |
| 7 | RTSA, RTSB | Request to Send; Output from SBC |
| 8 | CTSA, CTSB | Clear to Send; Input to SBC |
| 9 | RI | Ring Indicator; Not used - Not connected on the SBC |
| Shield | DE9 Shield | Connected to the SBC GND signal |
J4 - NVRAM Battery
Connect 3V battery for SRAM backup to this connector.
Important: If the SRAM battery backup is not desired, short J4 with a jumper. Do not leave this connector open.
| Pin | Signal Name | Description |
|---|---|---|
| 1 | VBAT | Positive terminal - +3V |
| 2 | GND | Negative terminal - ground |
J5, J6, J7 - RC2014 Bus
| Pin | Signal Name | Description | Pin | Signal Name | Description |
|---|---|---|---|---|---|
| J5-1 | A15 | Address A15; Output | |||
| J5-2 | A14 | Address A14; Output | |||
| J5-3 | A13 | Address A13; Output | |||
| J5-4 | A12 | Address A12; Output | |||
| J5-5 | A11 | Address A11; Output | |||
| J5-6 | A10 | Address A10; Output | |||
| J5-7 | A9 | Address A9; Output | |||
| J5-8 | A8 | Address A8; Output | |||
| J5-9 | A7 | Address A7; Output | |||
| J5-10 | A6 | Address A6; Output | |||
| J5-11 | A5 | Address A5; Output | |||
| J5-12 | A4 | Address A4; Output | |||
| J5-13 | A3 | Address A3; Output | |||
| J5-14 | A2 | Address A2; Output | |||
| J5-15 | A1 | Address A1; Output | |||
| J5-16 | A0 | Address A0; Output | |||
| J5-17 | GND | Ground | J6-1 | GND | Ground |
| J5-18 | VCC | Power Supply - +5V | J6-2 | VCC | Power Supply - +5V |
| J5-19 | /M1 | Machine Cycle One; Output | J6-3 | /RFSH | DRAM refresh; Output |
| J5-20 | /RESET | Reset; Output | J6-4 | N/C | Not connected |
| J5-21 | CPU_CLK | CPU Clock; Output | J6-5 | UART_CLK | UART Clock (1.8432 MHz); Output |
| J5-22 | /INT | Interrupt; Input | J6-6 | /BUSACK | DMA Bus Acknowledge; Output |
| J5-23 | /MREQ | Memory Request; Output | J6-7 | /HALT | Halt; Output |
| J5-24 | /WR | Write Request; Output | J6-8 | /BUSREQ | DMA Bus Request; Input |
| J5-25 | /RD | Read Request; Output | J6-9 | /WAIT | Wait; Input |
| J5-26 | /IORQ | Input/Output Request; Output | J6-10 | /NMI | Non-maskable Interrupt; Input |
| J5-27 | D0 | Data D0; Input/Output | |||
| J5-28 | D1 | Data D1; Input/Output | |||
| J5-29 | D2 | Data D2; Input/Output | |||
| J5-30 | D3 | Data D3; Input/Output | |||
| J5-31 | D4 | Data D4; Input/Output | |||
| J5-32 | D5 | Data D5; Input/Output | |||
| J5-33 | D6 | Data D6; Input/Output | |||
| J5-34 | D7 | Data D7; Input/Output | |||
| J5-35 | TXDA | Channel A, Transmit Data; Output | J7-1 | TXDB | Channel B, Transmit Data; Output |
| J5-36 | RXDA | Channel A, Receive Data; Input | J7-2 | RXDB | Channel B, Receive Data; Input |
| J5-37 | USR1 | User Pin 1, Not connected | J7-3 | USR5 | User Pin 5, Not connected |
| J5-38 | IEI | Interrupt Enable Input | J7-4 | USR6 | User Pin 6, Not connected |
| J5-39 | IEO | Interrupt Enable Output | J7-5 | USR7 | User Pin 7, Not connected |
JP1 - Serial Channel A Clock Select
| Position | Description |
|---|---|
| 1-2 (default) | 1.8432 MHz (115200 bps if using x16 mode) |
| 2-3 | Programmable using CTC channel 0 |
JP2 - Serial Channel B Clock Select
| Position | Description |
|---|---|
| 1-2 (default) | 1.8432 MHz (115200 bps if using x16 mode) |
| 2-3 | Programmable using CTC channel 1 |
Bill of Materials
Version 1.1
Easy Z80 project on Mouser.com - View and order all components except of the PCB.
Easy Z80 project on OSH Park - View and order the PCB.
| Component type | Reference | Description | Quantity | Possible sources and notes |
|---|---|---|---|---|
| PCB | Easy Z80 PCB - Version 1.1 | 1 | Refer to the RetroBrew Computers Board Inventory page for ordering information, or order from a PCB manufacturer of your choice using provided Gerber or KiCad files | |
| Integrated Circuit | U1 | Z80 CPU, CMOS, 40 pin DIP - Z84C00xxPEG | 1 | Mouser 692-Z84C0010PEG |
| Integrated Circuit | U2 | Z80 CTC, CMOS, 28 pin DIP - Z84C30xxPEG | 1 | Mouser 692-Z84C3010PEG |
| Integrated Circuit | U3 | Z80 SIO/0, CMOS, 40 pin DIP - Z84C40xxPEG | 1 | Mouser 692-Z84C4010PEG |
| Integrated Circuit | U4 | 512 KiB SRAM, 32 pin DIP - AS6C4008 | 1 | Mouser 913-AS6C4008-55PCN |
| Integrated Circuit | U5 | 512 KiB Flash ROM, 32 pin DIP - SST39SF040 | 1 | Mouser 804-39SF0407CPHE |
| Integrated Circuit | U6 | Microprocessor Supervisory Circuit - MAX693 | 1 | Mouser 584-ADM693ANZ; Possible alternatives: MAX693, LTC693, ADM691, MAX691, LTC691, ADM695, MAX695, LTC965, LTC1235 |
| Integrated Circuit | U7, U8 | Dual RS-232 Driver/Receiver - MAX232A | 2 | Mouser 595-TRS202EIN |
| Integrated Circuit | U9 | Simple Programmable Logic Device - ATF16V8B | 1 | Mouser 556-AF16V8B15PU |
| Integrated Circuit | U10, U11 | 4-by-4 Register File - 74HC670 | 2 | Mouser 595-CD74HC670E |
| Integrated Circuit | U12 | Dual Flip Flop - 74HC74 | 1 | Mouser 595-SN74HC74N |
| Oscillator | QG1 | 10 MHz, CMOS oscillator, Half Can | 1 | Mouser 774-MXO45HS-3C-10.0 |
| Oscillator | QG2 | 1.8432 MHz, CMOS oscillator, Half Can | 1 | Mouser 774-MXO45HS-3C-1.8 |
| LED | D1 | 3 mm, green LED indicator | 1 | Mouser 859-LTL-4231N |
| Tactile Button | SW1 | 6 mm tactile button, right angle | 1 | Mouser 653-B3F-3152 |
| Connector | J1 | DC Power Jack, 2mm | 1 | Mouser 806-KLDX-0202-A |
| Connector | J2, J3 | Sub-D DE9M, Right Angle, PCB mount | 2 | Mouser 806-K22X-E9P-N-99 |
| Connector | J4 | 2 Pin Header with Friction Lock | 1 | Mouser 571-6404562 |
| Pin Header | J5 - J7 | 40x2 Pin Header, 2.54 mm Pitch, Right Angle | 1 | Mouser 571-9-103326-0 |
| Capacitor | C1 - C14, C16 - C23 | 0.1 uF, MLCC, 5 mm Pitch | 22 | Mouser 594-K104K15X7RF53H5 |
| Capacitor | C24 | 47 uF, 25V, Aluminum Organic Polymer | 1 | Mouser 80-A750EK476M1EAAE40 |
| Resistor Array | RN1 - RN3 | 4.7 k, bussed, 5 pin SIP | 3 | Mouser 652-4605X-AP1-472LF |
| Resistor Array | RN4 | 4.7 k, bussed, 9 pin SIP | 1 | Mouser 652-4609X-AP1-472LF |
| Resistor | R1 | 470 ohm, axial | 1 | Mouser 603-MFR-25FRF52-470R |
| Resistor | R2 - R4 | 10 kohm, 1% tolerance, axial | 3 | Mouser 603-MFR-25FRF5210K |
| Resistor | R5 | 29.4 kohm, 1% tolerance, axial | 1 | Mouser 603-MFR-25FBF52-29K4 |
| Trimmer Resistor | RV1 | 2 kohm, through hole | 1 | Mouser 652-3362P-1-202LF |
| IC Socket | U1, U3 | 40 pin DIP | 2 | Mouser 517-4840-6000-CP |
| IC Socket | U4, U5 | 32 pin DIP | 2 | Mouser 517-4832-6000-CP |
| IC Socket | U2 | 28 pin DIP | 1 | Mouser 517-4828-6000-CP |
| IC Socket | U9 | 20 pin DIP | 1 | Mouser 517-4820-3000-CP |
| IC Socket | U6 - U8, U10, U11 | 16 pin DIP | 5 | Mouser 517-4816-3000-CP |
| IC Socket | U12 | 14 pin DIP | 1 | Mouser 517-4814-3000-CP |
| Oscillator Socket | QG1, QG2 | 4 pin DIP, Half Can | 2 | Mouser 535-1108800 |
Firmware Documentation
BIOS and OS
Easy Z80 is supported by RomWBW v2.9.1 and later. RomWBW includes BIOS, CP/M-80 2.2, Z-System, and a collection of utilities. It also should be possible to run FUZIX on this board.
SPLD Fuse Map
Easy Z80 uses an ATF16V8/GAL16V8 SPLD (U9) for address decode logic. The SPLD fuse map and the SPLD source code are provided in SPLD directory of this repository.
Release Notes
Changes
- Version 1.1
- Add pull-up resistors on the data bus (RN4 - 4.7k) to support Z80 interrupt mode 0
- Use 74HC series instead of 74HCT
- Remove C15
- Use RN reference for resistor arrays instead of RR
- Update silkscreen:
- Make RN1 reference and value visible
- Update silkscreen of headers footprints, so that JP1 and JP2 don't cover the traces
- Add project URL to the bottom silkscreen
- Version 1.0
- Initial version
Known Issues
- Version 1.0
- Top silkscreen: RR1 reference and value are not visible. It should read "RR1, 4.7k"
- Bottom silkscreen on JP1 and JP2 covers the trace connections, so they are not easily visible
- Bottom silkscreen: No project URL. Should be github.com/skiselev/easy_z80
- Board will not reset when C15 is populated. Workaround: Do not populate this capacitor
- Schematic and top silkscreen: Use 74HC series instead of 74HCT
Wishlist
- Version 1.0
- Add pull-ups on the data bus to support extension boards that were not designed for Z80 interrupt mode 2
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