bcichonski/bc16

I allways wanted to build 8bit computer, as i am to lazy to work with hardware, this is the closest thing to that

I have always wanted to build 8bit computer, as i am to lazy to work with hardware, this is the closest thing to that.

BC32

roadmap

0. smaller peripherals
1. fdd
2. memory extension
3. bcos upgrade
4. bdos development
5. new binary file format
6. new assembler
7. new blang compiler

architectural notes

OS

bcos v1.1

• some procedures from b compiler stdlib incorporated
• minor fixes
• still tape-only suport with for .btap files
• new code to recognize presence of floppy disk drive to boot their system

bdos v1

• disk operation system
  • micromode (the os itself just knows how to load and run executables)
• bfs file system
  • only files
  • but with some attributes

CPU

microprocessor: bc8182 (very small fixes regarding f register) 64kb address space 16 in/out ports no interrupts one extension slot (basically allows a device to use memory directly)

memory

memory: 32kb ~6kb rom + 26kb ram with option to extend in future

peripherals

same as BC16 plus

• real time clock 0x3
• random generator 0x4
• floppy disk drive 0x8

  • port 0x8 used for instructions and communication:

    • 0xf0 - ping with response with version of the drive: returns READY | FDVER1
    • 0xf1 - configure DMA - sets where drive can put read sector, always 128 bytes returns READY
    • 0xfa - set active drive A returns READY
    • 0xfb - set active drive B returns READY
    • 0xf2 imm8:t imm8:s - reads sector s from track t returns READY or CFGERROR or CMDERROR
    • 0xf3 imm8:t imm8:s - writes sector s from track t returns READY or CFGERROR or CMDERROR
    • 0xf4 - eject active drive
    • response codes:
      • READY: 0x10
      • FDVER1: 0x01
      • CFGERROR: 0xe1
      • CMDERROR: 0xe2

  • uses direct memory access to read entire sector

  • double drive for single side 3" floppy disks that has 64 tracks of 16 sectors of 128 bytes = 128 KB

BC16

architectural notes

OS

bcos v1.0 tape-only suport with for .btap files

CPU

microprocessor: bc8181 - bc8182 64kb address space 16 in/out ports no interrupts

memory

memory: 16kb 4kb rom + 12kb ram with option to extend in future

the bc8182 microprocessor

same as bc8181 but with some small errors fixed some extentions like 16bit arithmetic? or 8bit div/mod/mul

peripherals:

• terminal keyboard uses io ports 0x0

• terminal printer uses io ports 0x1

• cassette recorder uses io ports 0x2 ports 0x2 are used for manipulating recorder: valid commands to sent via 0x2 output port: 0x80 - load tape - set this bit and question for the name of the tape file to read will appear; only one of 0x80/0x40 flag can be set 0x40 - save tape - set this bit and question for the name of the tape file to save will appear; only one of 0x80/0x40 flag can be set 0x20 - start/stop moving recorder engine, initiates/ends read/write sequence 0x01 - reserved for writing or reading bit to/from the device
  0x10 - ready flag - if device is ready for reading next command 0x08 - error flag - ie when tape is full

  example session for writing to the tape: read 0x2 port

the bc8181 microprocessor

registers:

0xF 0xE PC - 16bit
0xD SS - address of STACK segment
0xC SI - 8 bit stack index goes down from memory top

0xB F - 8bit processor flags
 0x0 - ZERO
 0x1 - CARRY
 0x2 - NEGATIVE
 0x3 - OVERFLOW
0x1 A - 8bit accumulator
0x4 CI - 8bit register addressing C segment
0x5 DI - 8bit register addressing D segment
0x8 CS - 8bit register storing address of C segment
0x9 DS - 8bit register storing address of D segment

instuctions

instructions are 1 or 2 bytes long:
B0(HL)B1(HL)
bc8181 instruction set B0H:
0x0 - NOP               ;
0x1 - MOV rno,imm        ; r=imm
0x2 - MOV rno1,rno2      ; r1 = r2
0x3 - MOV rno1,(rno2, rno3)    ; r1 = mem(r2) , r2 can be CI or DI
0x4 - MOV (rno1,rno2), rno3   ; mem(r1) = r2
0x5 - CLC A
  0x0 - add imm          ; A += imm
  0x8 - add rno          ; A += r
  0x1 - sub imm
  0x9 - sub rno
  0x2 - and imm
  0xA - and rno
  0x3 - or imm
  0xB - or rno
  0x4 - xor imm
  0xC - xor rno
  0x5 - shl imm
  0x6 - shr imm
  0x7 - not A - only 1 byte
  0xD - inc A - only 1 byte!
  0xE - dec A - only 1 byte!
  0xF - not used for future extensions
0x6 - JMP t,(rno1,rno2)
  0x0 - if ZERO
  0x4 - if NOT ZERO
  0x1 - if CARRY
  0x5 - if NOT CARRY
  0x2 - if NEGATIVE
  0x6 - if NOT NEGATIVE
  0x3 - if OVERFLOW
  0x7 - if NOT OVERFLOW
  0x8-0xF is special mode where addres is CS:imm (its kind of short absolute jump)
0x7 - JMR t,imm7
  t like JMP, imm7 is 8bit signed value
  when t 0x8-0xF is special mode where rno is treated like imm7
0x8 - PSH rno
0x9 - POP rno
0xA - CAL 
  0x0 (rno1,rno2)
  0x8 imm16
0xB - RET
0xC - IN
 0x0-0x7 - rno, #imm
 0x8-0xf - rno1, #rno2
0xD - OUT imm,rno
 0x0-0x7 - #rno1, imm
 0x8-0xf - #rno1, rno2
0xE - NOP not_used
0xF - KIL

software

external assembler bc81asmc up to 1.1 (240317) external compiler bc of b language for bc8181-bc8182 cpu v 1.0.0 (240317) calc - basic calculator texted - basic line editor theodore - simple game