The P112 CPU Board

P112 Board

What is it?

The P112 is a stand-alone 8-bit CPU board. Typically running CP/M (tm) or a similar operating system, it provides a Z80182 (Z-80 upgrade) CPU with up to 1MB of memory, serial, parallel and diskette IO, and realtime clock, in a 3.5-inch drive form factor. Powered solely from 5V, it draws 150mA (nominal: not including disk drives) with a 16MHz CPU clock. Clock speeds up to 24.576MHz are possible.

Download Section



  1. Dimensions: 130 x 100mm (5.1 x 3.9 inch)
  2. Support for 5.25 and 3.5 inch diskette drives (up to 4 drives, mixed types)
  3. Z80182 CPU at 16MHz (12.228, 18.432 or 24.576MHz optional)
  4. 32kB flash ROM, in-board reprogrammable
  5. 64kB SRAM, upgradeable to 1MB
  6. Real-time clock/RAM, with on-board battery
  7. 5 (yes, five) serial IO ports, 2 as PC-AT compatible connectors, 3 as TTL outputs
  8. Parallel port, IBM compatible, with bidirectional ability
  9. Bus expansion/logic analyser socket
  10. Software included:
    Shareware DOS+ and CCP+ (replace CP/M)
    Shareware PPIP (replaces PIP)
    BIOS support for diskettes, parallel & RS232 serial ports
    ROM monitor, including debugger
The board is designed with a maximum of through-hole parts, to facilitate home assembly. As the CPU and IO chip are only available in 100-pin QFPs (and are not readily available in one-offs), we offer the board with these items (and 3 other small SMDs) pre-assembled. You can obtain the other parts locally, and assemble them yourself. Alternatively, we offer the board fully built up & tested.
Both options include a pre-programmed flash ROM, plus a 3.5 inch bootable disk with the above-mentioned software.
P112 was designed in 1996, and sales have now dwindled to virtually nothing. Consequently, I have reluctantly decided not to accept further orders for this product. I thank previous customers for their support. This page will remain up for information, and the download files will still be available.
2016: The circuit board layout is hereby placed in the public domain, under the GPL v2. Anyone is now free to have boards fabricated from these files, and/or to derive modified designs from them.
I have converted the layout to the current Altium release (16), many PCB fabricators can accept Altium files directly.

Parts List (for home builders)

 22pF ceramic           4       C1      C2      C25     C26
 120pF ceramic          1       C12
 100nF bypass           14      C3      C15     C16     C17     C18
                                        C19     C20     C21     C22     C23
                                        C24     C28     C29     C30
 1uF, 16V tant.         9       C4      C5      C6      C7      C8
                                        C9      C10     C11     C27
 22uF, 10V tant.        2       C13     C14
 7x220 respack          1       U13
 7x2k2 respack          1       U14
 7x47k respack          2       U16     U17
 4k7 resistor           1       R11
 10k resistor           3       R5      R7      R10
 27k resistor           1       R9
 47k resistor           8       R1      R2      R3      R4      R6
                                        R8      R12     R13
 2-pin Hdr              2       P5      P11
 3-pin Hdr              3       P1      P12     P13
 5-pin Hdr              2       P2      P6
 2x2-pin Hdr            1       P3
 2x5-pin Hdr            2       P4      P8
 2x10-pin Hdr           1       P14
 2x13-pin Hdr           1       P7
 2x17-pin Hdr           2       P9      P10
 PCB jumper             10
 DIN48 skt.             1       J1              (3x16-way half-DIN skt)
 32DIP skt.             3       U2      U3      U4
 32kHz crystal          1       Y2              (RTC crystal)
 16MHz crystal          1       Y1              Parallel resonant (CPU clock)
 24MHz crystal          1       Y3              Parallel resonant (IO chip clock)
*BAR43C diode           1       D1              (Schottky)
*BAR43  diode           1       D2              (Schottky)
*BCW71  transistor      1       Q1
 28F256A                1       U4              (Intel Flash ROM, programmed)
 74HCT00                1       U5
 74ACT02                1       U8
 74ACT139               1       U11
 62256                  2       U2      U3      (Static RAM, 32kB)
 DS1202                 1       U6              (Dallas RTC chip)
*FDC37C665IR            1       U9              (SMC Super-IO chip)
 LT1133                 2       U7      U10     (Linear Technology RS232 Tx/Rx)
 NMF0512S               1       U12             (Newport Components Flash ROM power)
 TL7705ACP              1       U15             (Texas Insts. Reset genr.)
*Z8018216               1       U1              (Zilog CPU chip)
 3.7V battery           1       B1              (Lithium Thionyl Chloride, 1/2AA)
Parts prefixed * are pre-installed on the board.

The Fine Print

If you have purchased this board fully assembled, D-X Designs Pty Ltd warrants it in respect of faulty components or workmanship, for a period of ninety days from purchase, providing it has not been subject to damage or abuse. Defective boards must be returned, freight prepaid, to our Australian address. We will (at our option) repair or replace such boards, and return them to you.
If you have purchased a part-assembled board, we cannot guarantee performance, since the conditions of handling and assembly of parts are beyond our control.
To the extent permitted by applicable laws, this warranty excludes all others express or implied, and defines our complete liability. This warranty, and the associated contract of purchase, shall be governed by the laws of the State of Western Australia.
This board, and its accompanying software, are not designed or intended for use in safety-critical or life-support applications. No liability of any kind is accepted for such use. See also the file LICENSE.TXT on the accompanying diskette, with respect to software (this file is the text of the GNU General Public License).
This board is not a complete electronic system, but a component thereof. As such, it does not include shielding measures to limit spurious electromagnetic emissions. It is the responsibility of the person constructing a complete apparatus, to take such precautions as may be necessary to comply with relevant regulations regarding such emissions.

Software Updates

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New software releases for the P112 board will be downloadable from here.....
All software, & the PCB layout, are offered under the GNU General Public License

Note: Updates of my ROM code have been removed. All updates to date (March 1997) are now incorporated in the main ROM-code archive (see the Download Section)

Ready-to-use Binaries

If you have built a P112 from a bare board, this is what you need to get it up & running.
To burn a system ROM, use either of the ROM files
1996 version or 1997 version. The later one has a few extra bugfixes, but the earlier is more widely used. Your choice. You will need access to a ROM programmer for this.
To make a boot disk, download the disk image and a copy of rawrite. "rawrite" is taken from the Red Hat Linux 6.2 distribution. Format a 1.44MB floppy with MS-DOS, use rawrite to copy the disk image to it, and you're ready to go.
A problem has been reported in using these SMC I/O chips with Windows: the FIFO buffers can malfunction. It is not known whether this will affect the P112 board: but developers of high-speed communications software should be aware of it.
See (Both these links appear broken - 2004):

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