8-bit computer simulation for the BBC micro:bit The simulator demonstrates 8-bit programming with the ability to save and load programs: it also works as a simple binary to decimal or hexadecimal translator. http://pdbperks.github.io/altair/
Tilt the board to select the active column and row for data LED.
The button functions:
Button A: press to toggle data LED. Long press to clear all data LEDs.
Run: Hold Button A, press button B once. Release both buttons.
Load: Hold Button A, press button B twice. Release both buttons.
Save: Hold Button A, press button B thrice. Release both buttons.
Trace: Hold Button A, press button B four times. Release both buttons.
Reload sample code: Hold Button A, press button B five times. Release both buttons.
Halt program execution: hold Button A.
Button B: press for decimal. Long press hexadecimal.
Write. PC++: Hold Button B, press button A once. Release both buttons.
PC--. Read: Hold Button B, press button A twice. Release both buttons.
Goto: Hold Button B, press button A thrice. Release both buttons.
Here is a list of the implemented operating codes using the Accumulator, Register B, Register C, and zeroflag.
I am providing two address bytes although one would be perfectly functional since program memory is currently set at 256 bytes.
No further additions are now envisaged due to memory allocation limits.
| Decimal | Hex | Binary | Mnemonic | Bytes | Action |
|---|---|---|---|---|---|
| 7 | 0x07 | 0000 0111 | RLC | 1 | Accumulator bit shift left |
| 13 | 0x0D | 0000 1101 | DECC | 1 | Register C - 1 |
| 15 | 0x0F | 0000 1111 | RRC | 1 | Accumulator bit shift left |
| 50 | 0x32 | 0011 0001 | STA | 3 | Store Accumulator in address |
| 58 | 0x3A | 0011 1010 | LDA | 3 | Load Accumulator with contents of address |
| 60 | 0x3C | 0011 1100 | INRA | 1 | Accumulator + 1 |
| 61 | 0x3D | 0011 1101 | DCRA | 1 | Accumulator - 1 |
| 71 | 0x47 | 0100 0111 | MOVBA | 1 | Move Accumulator to Register B |
| 79 | 0x4F | 0100 1111 | MOVCA | 1 | Move Accumulator to Register C |
| 118 | 0x76 | 0111 0110 | HLT | 1 | Halt program execution |
| 128 | 0x80 | 1000 0000 | ADDB | 1 | Add Register B to Accumulator |
| 160 | 0xA0 | 1010 0000 | ANAB | 1 | Bitwise Accumulator & Register B |
| 168 | 0xA8 | 1010 1000 | XRAB | 1 | Bitwise Accumulator ^ Register B |
| 175 | 0xAF | 1010 1111 | ANAA | 1 | Bitwise Accumulator ^ Accumulator |
| 176 | 0xB0 | 1011 0000 | ORAB | 1 | Bitwise Accumulator | Register B |
| 194 | 0xC2 | 1100 0010 | JNZ | 3 | Jump to address if zeroflag false |
| 195 | 0xC3 | 1100 0111 | JMP | 3 | Jump to address |
On reboot, the emulator will have a clear memory.
If you load a program (A, 3 clicks B) it will load the sample program given in the Altair manual.
If you have saved your own program then that will be loaded.
Use (A, 5 clicks B) to revert to the sample program.
You can toggle a trace feature for the contents of the Accumulator (A, 4 clicks B) which is useful for debugging.
I have added a program at memory address 0x10 (16) to demonstrate JNZ op code.
I have also changed the memory addresses used by the sample program so that data examples are preloaded with the code:
add contents of memory addresses 12 and 13, store the answer in memory address 15.
| Address | Mnemonic | Binary | Action |
|---|---|---|---|
| 0 | LDA | 0011 1010 | Load Accumulator with contents of address |
| 1 | 0000 1100 | Address (12) | |
| 2 | 0000 0000 | Address | |
| 3 | MOVAB | 0100 0111 | Move accumulator to Register B |
| 4 | LDA | 0011 1010 | Load Accumulator with contents of address |
| 5 | 0000 1101 | Address (13) | |
| 6 | 0000 0000 | Address | |
| 7 | ADDB | 1000 0000 | Add Register B to Accumulator |
| 8 | STA | 0011 0010 | Store Accumulator in address |
| 9 | 0000 1111 | Address (15) | |
| 10 | 0000 0000 | Address | |
| 11 | HLT | 0111 0110 | Halt program |
| 12 | 0000 0001 | Data | |
| 13 | 0000 0010 | Data | |
| 14 | 0000 0100 | Data | |
| 15 | 0000 0000 | Data | |
| 16 | LDA | 0011 1010 | Load Accumulator with contents of address |
| 17 | 0000 1110 | Address (14) | |
| 18 | 0000 0000 | Address | |
| 19 | MOVCA | 0100 1111 | Move accumulator to Register C |
| 20 | INRA | 0011 1100 | Accumulator + 1 |
| 21 | DECC | 0000 1101 | Register C - 1 |
| 22 | JNZ | 1100 0010 | Jump to address if zeroflag false |
| 23 | 0001 0100 | Address (20) | |
| 24 | 0000 0000 | Address | |
| 25 | STA | 0011 0010 | Store Accumulator in address |
| 26 | 0000 1111 | Address (15) | |
| 27 | 0000 0000 | Address | |
| 28 | HLT | 0111 0110 | Halt program |