Micral P2

Technical detail about the Bull Micral P2 computer
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For history about work on this machine, see the related blog posts by clicking the tags above.

Full-res pictures and ROM dumps are also available in the Downloads category

Bull Micral P2

Specs

Specs:

  • Z80 CPU at 5 MHz
  • 64k RAM
  • 2 double-density 80 track floppy drives
  • Internal modem
  • Probable teletext terminal cababilities

Ports:

  • Phone cord with French T-shaped landline plug
  • Peritel (= French SCART) video out, maybe RGB?
  • Composite video out, SMB connector
  • DB25 V24 / serial port
  • Printer port, 36 pin
  • Cassette port, DIN5

There are two 1.6A fuses at the back.

Motherboard

Motherboard reference: R2E 371625 BB1

Motherboard

Chips:

Marking Manufacturer Reference Role
U41 SGS Z8400BB1 Z80 B CPU (goes up to 6 MHz)
U42 SMC FD1797 Floppy Controller
U6 Philips SAA5070 Multifunction
U9 SMC KR3600-017 Keyboard Controller
U12 Philips SAA5120 Not sure, Videotext related
U34 Philips SAA5150 Not sure, Videotext related
U62 Signetics SCN2661A UART
U52 SMC FDC9229BT Floppy interface
U24-27, U36-39 Mitsubishi M5K4164P-15 64k x 1 DRAM
U21, U32 INMOS IMS1420P55 4k x 4 SRAM, for video
U13 National Semi DM74S472AN “9112610”, 4k PROM, for addressing?
U22 Signetics N82S147AN “9112710”, 4K PROM, for addressing?
U29 NEC D2716D 2K x 8 Boot ROM
U30 NEC D2716D 2K x 8 Keyboard ROM

Notable parts:

  • QZ1: 4.9152 MHz quartz
  • QZ2: 16 MHz quartz
  • QZ3: 24 MHz quartz
  • K1: Little 12V relay
  • There are two 75189 RS-232 buffers but only one 75188

Note: U29 is in a 28 pin socket, which might accept 2764 ROM chips.

Connectors:

Marking Type Pins Role
J1 N/A 2 * 32 Unpopulated, Role unknown
J2 HE10 26 Keyboard interface
J3 HE10 10 Video out, Peritel
J4 SMB 2 (coax) Video out, Composite
J5 HE10 36 Printer
J6 SUB-D 25 Serial/V24, female connector
J7 HE10 34 Floppy
J8 HE10 5 Cassette, goes to DIN-5
J9 SMB 2 (coax) Video to monitor
J10 3.96? 7 keyed Power input, with a key
J11 HE10 20 Modem
J12 HE10 5 Unknown, maybe serial

There’s a dozen jumpers too.

Boot Monitor

The boot monitor initializes hardware, runs basic self test then shows a prompt.

If the autotest succeeds, it will show AUTO-TEST : OK. Otherwise it will be AUTO-TEST : followed by error codes:

  • 0: Video RAM
  • 1: Main RAM
  • 2: FDC
  • 3: Serial
  • 4: Timer

Prompt commands:

  • CR : default boot (drive 0)
  • B<drive>,<sector> : boot drive,sector
  • * : transparent terminal, prints typed characters. Press ESC to exit
  • G<address> : execute at address (hex)
  • M : memory submenu
    • D<start>,<end> : hex dump memory range (16 bytes/line)
    • M<addr> : modify memory byte-by-byte (’.’ to quit)
    • I<port> : read and display I/O port value
    • O<port>,<value>: write byte to I/O port
    • G<addr> : execute at address
    • R : return to main prompt

Contrary to other machines, there’s a special loader program in the boot ROM which reads data from the disk and acts upon its contents. It first checks the first sector for settings, then reads the following ones as blocks with specific commands.

The format is: [block size][command][address_h][address_l][zero][contents...]. Block types are:

  • 0xC2: data record. Copy data at given address
  • 0xC6: copy a trampoline code into ram, jump to it and disable ROM
  • 0xD2: error, abort loading
  • Other values between 0xC1 and 0xDB are valid but not interpreted and the block is skipped

Notes:

  • All the commands should be typed in caps. Lower case characters do not work.
  • These were obtained through automated disassembly and have yet to be confirmed.

Disassembly is available here: https://github.com/fstark/micral-p2

Power Supply

PSU

Made by HiTRON, model HSC55-044. It’s probably a custom order for Bull, as mine has a #0084 serial.

It works fine but 2 filtering caps made by RIFA exploded a long time ago. The smell lingers… The heatsink as a greased back, but it doesn’t touch anything in the chassis except for my fingers during disassembly.

Output voltages:

  • 12V 3A
  • 5V 5A
  • -12V 0.2A

Fuses:

  • F1: 250V 2A fast blow, 30mm long

Filtering capacitors:

Marking Brand Reference Value Class Length Width Lead pitch
C1 RIFA PME271M510 0.1 µF X2 24mm 5mm 20mm
C2 RIFA PME271M510 0.01µF X2 18mm 5mm 15mm
C16 RIFA PME271M610 0.01µF X2 18mm 7.5mm 15mm

Replacements: 2 * 103MKP275KE, 1 * B32933A3104K000

Floppy Drives

Floppy Drive PCB

The two floppy drives are manufactured by Toshiba, and have the part number MKM0262E002. They’re quite similar to the FDD5401 model, but might be a custom order for Bull. I’ve seen similar looking drives used later in the Bull Micral 30 PC compatible.

Specs:

  • 80 tracks
  • 2 heads
  • 300 RPM
  • 96 TPI

CP/M

The P2 uses CP/M 2.2.

Partial BIOS disassembly is available here: https://github.com/Altomare/micral-p2-cpm

Disk geometry:

  • 2 sides
  • 80 tracks per side
  • 16 sectors per track
  • 256 bytes per sector
  • MFM encoding
  • 3 tracks reserved for CP/M
  • Block size = 2048
  • Maximum directory entries = 128
  • Physical skew factor = 1
    • One sector between each consecutive one on the disk: 1, 9, 2, 10, 3…
  • No sector translation table for the BDOS
  • Disk fill order = CHS

To-Do

  • Weight
  • Measurements
  • Modem, keyboard
  • Motherboard
    • Document jumpers
    • Pinouts
    • Check PAL/GAL references and dump them
  • Video
    • Display size and characteristics (columns, lines)
    • Is there a bitmap mode?
  • Floppy
    • Dump & upload CP/M disk
    • Document geometry