2 layers99.1 × 99.1 mm
100x100mm Computer Perf Board
giraffeics/BEEBA
An 8-bit computer built using 7400 Series discrete logic chips.
1,283 parts2
2 layers99.1 × 99.1 mm
Basic IO Board
giraffeics/BEEBA2An 8-bit computer built using 7400 Series discrete logic chips.
- Size
- 99.1 × 99.1 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 57
- Nets
- 112
- Pads
- 310
- Tracks, vias
- 822, 25
- Pours
- 2
- Routed
- Yes
- KiCad
- KiCad 4
- Created
- 14 Oct 2017
- Updated
- 14 Oct 2017
Overview
Basic IO Board is an open-source printed circuit board by giraffeics, from the giraffeics/BEEBA repository on GitHub. It is a 2-layer board of 99.1 × 99.1 mm with 57 parts on 112 nets, routed with 822 tracks and 25 vias.
It is built around the 74LS373SC, 74LS240DC and 74LS14PC. Its parts include 21 resistors, 17 diodes, 9 ICs, 3 switches and 1 capacitor. It belongs with the retro computing and games boards of this library.
Main components
3
74LS373SC
--55℃~+125℃ 1 2.6mA 24mA 38ns@5V,150pF 4.75V~5.25V 74LS 8 Output enable Tri-State - Buffers, Drivers, Receivers, Transceivers ROHSTexas InstrumentsBuffers, Drivers, Receivers, Transceivers74LS240DC
--55℃~+125℃ 1 15mA 18ns@5V,45pF 24mA 29mA 4.75V~5.25V 74LS Output enable Schmitt trigger Tri-State - Buffers, Drivers, Receivers, TransceiversTexas InstrumentsBuffers, Drivers, Receivers, Transceivers
74LS14PC
PDIP-14InvertersTexas Instruments
README
README.mdBEEBA
An 8-bit computer built using 7400 Series discrete logic chips.
Repository Layout
The "CAD" folder contains all design files for the printed circuit boards. These are KiCAD documents. The "Assembler" folder contains the C++ source code for the assembler, as well as the list of register names and some programs written in BEEBA assembly language. The assembler can be compiled with MinGW on Windows, and has not been tested on other compilers or operating systems.
Assembly Language
Assembly language programs can be in any plain-text file format. The language is not case-sensitive. Each instruction copies eight bits of data from one register location to another. A line of code can follow one of three formats:
COPY [read location] TO [write location]
Reads one byte of data from the register specified by [read location], writes data to the register specified by [write location].
SET [write location] TO [data]
Writes a byte of data specified by [data] to the register specified by [write location]. [data] can be a two-digit hexadecimal number or a marker.
MARK [marker name]
Marks the instruction position that corresponds to the following line of code. This does not represent an actual instruction. [marker name] can be referenced by SET instructions before or after the location of the marker, using a colon to specify which byte of the marker's location to use. This ranges from 0 (least significant) to 2 (most significant).
For all of these, any text after the last parameter will be ignored. However, it must be separated by a space or tab from the last parameter.
Register names are listed in REGISTER_NAMES.txt. The assembler uses this file to convert names to addresses while compiling programs.
Using The Assembler
To use the assembler, simply drag assembly source files onto the compiled executable.
As BEEBA uses two physical ROM chips to store 16-bit-wide instructions, the assembler will output two .bin files. One of these is loaded onto the ROM chip on the left, the other is loaded onto the ROM chip on the right. They are named accordingly.
Known Issues
When writing a constant to a register, the value will be corrupted unless the same data is sent to another register in the next instruction. The current workaround is to send data to NULL, which is an unused register.
The NES controller interface board cannot read the state of the A button. Pannenkoek2012 would love this.
The "Basic IO Board"'s input does not work at all. This was caused by oversights during the transition from TTL to CMOS. Output is still fully functional.
Parts
57| Qty | Value | Footprint | References |
|---|---|---|---|
| 19 | 270Ω | Resistors_ThroughHole:Resistor_Horizontal_RM10mm | R0, R1, R2, R3, R4, R5, R6, R10, R11, R12, R13, R14, R15, R18, R19, R20 +3 |
| 16 | Led_Small | LEDs:LED-3MM | D0, D1, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, D14, D15 |
| 4 | 1pin | Connect:1pin | MOUNT 1, MOUNT 2, MOUNT 3, MOUNT 4 |
| 3 | 74LS373 | Housings_DIP:DIP-20_W7.62mm | U1, U2, U8 |
| 2 | 74LS138 | Housings_DIP:DIP-16_W7.62mm | U4, U5 |
| 2 | 74LS240 | Housings_DIP:DIP-20_W7.62mm | U6, U7 |
| 2 | CONN_01X12 | Socket_Strips:Socket_Strip_Straight_1x12 | H1, H2 |
| 2 | DIPS_08 | dip-s:DIPS-DS08 | SW1, SW2 |
| 1 | 10KΩ | Resistors_ThroughHole:Resistor_Horizontal_RM10mm | R16 |
| 1 | 10µF | Capacitors_ThroughHole:C_Radial_D5_L11_P2 | C1 |
| 1 | 1KΩ | Resistors_ThroughHole:Resistor_Horizontal_RM10mm | R17 |
| 1 | 74LS14 | Housings_DIP:DIP-14_W7.62mm | U3 |
| 1 | 74LS244 | Housings_DIP:DIP-20_W7.62mm | U9 |
| 1 | LED_RCBG | LEDs:LED-RGB-5MM_Common_Cathode | D16 |
| 1 | SW_PUSH | custom:switch_tactile_6mm | SW3 |
Questions
How big is the Basic IO Board PCB?
It measures 99.1 × 99.1 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Basic IO Board use?
57 parts, built around the 74LS373SC, 74LS240DC and 74LS14PC. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the Basic IO Board KiCad files?
From the giraffeics/BEEBA repository on GitHub, at the commit this page was made from: the board is CAD/Basic IO Board/Basic IO Board.kicad_pcb. PCBKit opens the board in the browser, with nothing to install.
Can I use the Basic IO Board design in my own project?
Its repository states no licence, so its author keeps all rights: ask giraffeics before reusing the design.
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