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Breadboard Instructions
The first version of this computer was designed on a breadboard. The first video on YouTube explains the design of the breadboarded circuit. I have kept the bill of materials and table of pin-to-pin connections for the original breadboarded circuit for posterity.
Note that the design of the current z80ctrl board has diverged from this initial design considerably, and no attempt has been made to retain compatibility with the breadboard design. You will most likely need to check out an older commit from February 2018 or earlier in order to get the software to work with the circuit described below.
- Zilog Z84C010PEG 10MHz Z80 CPU
- Alliance AS6C4008 512KB SRAM chip
- Atmel ATmega1284p AVR microcontroller
- Microchip MCP23S18 SPI I/O expander
- 74HCT74 dual D-type flip-flop
- LM1117 3.3V regulator
- Silicon Labs CP2102 USB-to-TTL serial breakout
- Pololu ls01a 4 channel level shifter
- Pololu sdc01a microSD breakout
- 20MHz crystal with 20 pf load caps for AVR
- Various 0.01uf bypass and 10uf filter caps
The prototype has been built on two full-size breadboards using dupont wire. In lieu of a schematic for now, here is a table of connections. Pin names are followed by pin numbers are in parentheses. Please refer to notes after each table for connections marked with an asterisk.
| Z80 | 74HCT74 | Atmega1284P | MCP23S18 | AS6C4008 | Power |
|---|---|---|---|---|---|
| A0 (30) | PA0 (40) | A0 (12) | |||
| A1 (31) | PA1 (39) | A1 (11) | |||
| A2 (32) | PA2 (38) | A2 (10) | |||
| A3 (33) | PA3 (37) | A3 (9) | |||
| A4 (34) | PA4 (36) | A4 (8) | |||
| A5 (35) | PA5 (35) | A5 (7) | |||
| A6 (36) | PA6 (34) | A6 (6) | |||
| A7 (37) | PA7 (33) | A7 (5) | |||
| A8 (38) | GPA0 (20) | A8 (27) | |||
| A9 (39) | GPA1 (21) | A9 (26) | |||
| A10 (40) | GPA2 (22) | A10 (23) | |||
| A11 (1) | GPA3 (23) | A11 (25) | |||
| A12 (2) | GPA4 (24) | A12 (4) | |||
| A13 (3) | GPA5 (25) | A13 (28) | |||
| A14 (4) | GPA6 (26) | A14 (3) | |||
| A15 (5) | GPA7 (27) | A15 (31) | |||
| GPB5 (8) | A16 (2) | ||||
| GPB6 (9) | A17 (30) | ||||
| GPB7 (10) | A18 (1) | ||||
| D0 (14) | PC0 (22) | DQ0 (13) | |||
| D1 (15) | PC1 (23) | DQ1 (14) | |||
| D2 (12) | PC2 (24) | DQ2 (15) | |||
| D3 (8) | PC3 (25) | DQ3 (17) | |||
| D4 (7) | PC4 (26) | DQ4 (18) | |||
| D5 (9) | PC5 (27) | DQ5 (19) | |||
| D6 (10) | PC6 (28) | DQ6 (20) | |||
| D7 (13) | PC7 (29) | DQ7 (21) | |||
| M1# (27) | PB1 (2) | ||||
| MREQ# (19) | PD3 (17) | CE# (22) | |||
| IORQ# (20) | 1PRE# (4) | PD2 (16) | |||
| RD# (21) | PD5 (19) | OE# (24) | |||
| WR# (22) | PD4 (18) | WE# (29) | |||
| RFSH# (28) | |||||
| HALT# (18)* | PB2 (3)* | GND* | |||
| WAIT# (24) | 1Q# (6) | ||||
| INT# (16) | GPB0 (3) | ||||
| NMI# (17) | GPB1 (4) | ||||
| RESET# (26) | GPB2 (5) | ||||
| BUSREQ# (25) | GPB3 (6) | ||||
| BUSACK# (23) | GPB4 (7) | ||||
| CLK (6) | PD6 (20) | ||||
| 1CLR# (1) | PD7 (21) | ||||
| 1D (2) | GND | ||||
| 1CLK (3) | GND | ||||
| 2CLR# (13) | 5V | ||||
| 2D (12) | 5V | ||||
| 2CLK (11) | 5V | ||||
| 2PRE# (12) | 5V | ||||
| PB4 (5) | CS# (12) | ||||
| RESET# (16) | 5V | ||||
| SCK (8) | SCK (13) | ||||
| MISO (7) | SO (15) | ||||
| MOSI (6) | SI (14) | ||||
| PB3 (4) | |||||
| XTAL1 (13)* | |||||
| XTAL2 (12)* | |||||
| +5V (11) | VCC (14) | VCC (10) | VDD (11) | VCC (32) | 5V* |
| GND (29) | GND (7) | GND (11) | VSS (1) | VSS (16) | GND* |
Notes:
- HALT# connected to PB6 through a diode:
PB6 ->|- HALT#. PB6 is also connected through a momentary push button to ground. - Atmega1284p XTAL1 and XTAL2 connected to 20MHz full swing crystal oscillator with 20 pf load capacitors to GND on each pin.
- Each chip has a 0.1uf bypass capacitor from 5V to GND.
| Atmega1284p | LS01A | SDC01A | LM1117T-3.3V | Power |
|---|---|---|---|---|
| SCK (8) | H1 (2) | |||
| MISO (7) | H2 (3) | |||
| MOSI (6) | H3 (4) | |||
| PB3 (4) | H4 (5) | |||
| L1 (9) | SCLK (5) | |||
| L2 (8) | DO (4) | |||
| L3 (7) | DI (3) | |||
| L4 (6) | CS# (6) | |||
| VCC (10) | HV (1) | INPUT* | 5V | |
| LV (10) | VDD (2) | OUTPUT* | 3V | |
| GND (11) | GND (1) | GND* | GND |
Note: Input and output pins of LM117T-3.3V each have 10uf filter capacitor to GND.
| ATmega1284p | CP2102 | Power |
|---|---|---|
| RESET# (9)* | DTR* | 5V, GND* |
| RXD0 (14) | TXO | |
| TXD0 (15) | RXI | |
| VCC (10) | VCC | 5V |
| GND (11) | GND | GND |
Note: RESET# is connected to DTR through a 0.1uf capacitor: RESET# -||- DTR. RESET# is also connected through a 10K pullup resistor to 5V and through a momentary push button to GND.