FEL-1 = Fred II Experimental Language, version 1.
The FEL-1 Pseudo command syntax described here is used in the 'Fred demo' running on the FRED 1.5.
This info is also available online on the Emma 02 site.
| aaa | 12 bit address |
| kk | 8 bit constant |
| l | 4 bit constant |
| n | 4 bit constant |
| x | Register number Vx (x = 0 to F) |
| y | Register number Vy (y = 0 to F) |
| z | Register number Vz (y = 0 to F) |
| [8aa] | Memory value of address aa within page 8 (RAM) |
| [Vy] | Memory value of address in register Vy within in page 8 (RAM) |
| F= | Tone frequency |
| . | Not used, value doesn't matter |
| 1..9, A..F | Hexadecimal digits |
| 5xkk | ADD | Vx, kk | Vx = Vx + kk |
| 8xy4 | ADD | Vx, Vy | Vx = Vx + Vy, V0 is carry / not borrow |
| 8xy2 | AND | Vx, Vy | Vx = Vx AND Vy |
| 1aaa | CALL | aaa | Call subroutine at aaa. The subroutine must end in 026E (which is the 'FEL-1' equivalent of RETURN) |
| 0078 | CLS | Clear display | |
| 7x4B | DELAY | Vx | Vx Delay (Tape On, Speaker off) |
| 9xyl | DRW | Vx, Vy, l | Draw pattern, x = pattern address in page 3, y = tv cell address, l number of lines |
| 7F6F | INCA | RA = RA + 1 | |
| Ex8D | INP6 | Vx | Vx = INP 6 |
| Faaa | JP | aaa | Jump to address aaa |
| 0268 | KEY | OFF | Switch hex keypad off |
| Ex7A | KEY | Vx | Wait for key press and return in Vx |
| 7x52 | LD | B, [RA], Vx B, [A], Vx |
Convert Vx to 3 digit decimal at A, A+1, A+2 |
| Aaaa | LD | RA, aaa A, aaa |
RA = aaa |
| Baaa | LD | RB, aaa B, aaa |
RB = aaa |
| 7x2A | LD | RA.0, Vx A.0, Vx |
RA.0 = Vx |
| 7x30 | LD | RA.1, Vx A.1, Vx |
RA.1 = Vx |
| 7x34 | LD | RB.0, Vx B.0, Vx |
RB.0 = Vx |
| 2xkk | LD | Vx, kk | Vx = kk |
| 7x38 | LD | Vx, RA.0 Vx, A.0 |
Vx = RA.0 |
| 7x3B | LD | Vx, RA.1 Vx, A.1 |
Vx = RA.1 |
| 7x1E | LD | Vx, [RA] Vx, [A] |
Vx = [RA] |
| 7x21 | LD | Vx, [RB] Vx, [B] |
Vx = [RB] |
| 7x24 | LD | [RA], Vx [A], Vx |
[RA] = Vx |
| 7x27 | LD | [RB], Vx [B], Vx |
[RB] = Vx |
| 8xy1 | OR | Vx, Vy | Vx = Vx OR Vy |
| Ex91 | OUT4 | Vx | OUT 4 with Vx |
| Ex8F | OUT6 | Vx | OUT 6 with Vx |
| 022F | PUSH | Push V0-VF, A, B to 01E0-EF, F0-F3 | |
| 026E | RETURN | Return from subroutine CALL | |
| 4xkk | RND | Vx, kk | Vx = random AND kk |
| 8xy6 | SHR | Vx, Vy | Vx = Vy SHR, V0 is carry / not borrow |
| 7x3E | SHL4 | Vx | Vx = Vx SHL 4 |
| 7x41 | SHR4 | Vx | Vx = Vx SHR 4 |
| E.8A | SK3 | Skip next instruction if EF3 = 1 | |
| Ex80 | SKP | Vx | Read key if available if not skip next instruction |
| E.87 | SKT | Skip next instruction if tape is stopped | |
| 3xkk | SNE | Vx, kk | Skip next instruction if Vx != kk |
| Cxy0 | SNE | Vx, Vy | Skip next instruction if Vx != Vy |
| 8xy5 | SUB | Vx, Vy | Vx = Vx - Vy, V0 is carry / not borrow |
| 8xy7 | SUBN | Vx, Vy | Vx = Vy - Vx, V0 is carry / not borrow |
| 0aaa | SYS | aaa | Call CDP1801 code at aaa. The subroutine must end in a RET (D4) |
| 6.kk | TAPE | kk | Tape Controller - kk = code to write |
| E.93 | TAPE | READ | Read tape to [RA] and onwards |
| E.A0 | TAPE | WRITE | Write to tape from [RA] to 06FF |
| Dxy0 | TONE | Vx, Vy | Vx Tone, Vy Delay (Tape on speaker off) |
| 025C | VIDEO | ON | Video display enabled |
| 0240 | VIDEO | OFF | Video display disabled |
| 8xy3 | XOR | Vx, Vy | Vx = Vx XOR Vy |