MK-83

The board SBC Italian MK-82 was a clone of the original Ferguson BigBoard I, which was designed to fulfill the function of all-purpose programmable computer. Subsequent releases of articles supplementary to the U.S. holders of the original card in the journal Microcornucopia cloner has allowed the Italian to make interesting and unique modifications to achieve that in Italy it was called MK-83: draw a card identical to the MK-82 that were been implemented in a processor Z80A or Z80B operating at the clock frequency of the system, respectively, 4 or 6 MHz, a floppy disk controller to enable the management of double-sided double-density drive with both 8 "by 5.25" with its 50pin IDC connectors and 34pin onboard, and the ability to have an onboard memory of 256Kbyte (by 32 Ics type 4164).

Have existed at least 3 variations of the card itself MK83 born as a variation from the card MK82 copy of the original American Bigboard Ferguson 1. Carry the following differences:

MK83 ver. A (ex-CNR PISA) to implement a higher capacity memory disks was added in 1797 with a SMC chip separator external data FDC9229BT and related JB10 jumpers to set the delay on the precompensation in writing. In order to make best use of the double density (MFM) with 8 drive "was brought to the clock frequency of 4 MHz system (taking the clock from pin 5 of U96) and inserting the Z80 series components of type A. In addition, The following IC were changed: U97 = 7406; U98 = FDC9229BT; U99 = LS243; U100 = LS243. The EPROM is still kind of in 2716 and are still Dram IC type 4116. As I came into possession in December 2012. Has No. 2 EPROM type 2716 with firmware version 4.2 that is loaded into memory at address F800H (not to know if the firmware is loaded into memory then interacts with the contents of the EPROM performing their switch bank). I do not have floppy disk operating system CP / M, but through the R command available in the firmware you can manually read from standard 128 Bytes sectors.

This version ARRANGE wiring diagrams do not exactly copied in 1984 by the CNR in Pisa.

MK83 ver. B ("paid" by Fabio di Modena): in addition to changes introduced in version A, the clock frequency of the system was raised to 6 MHz (by changing the counting U96 with an additional quartz) and inserting the Z80 series components of type B . component U87 = LS02 was on the PCB moved between the CPU and Z80 U81 so that you can place in the space next to the Z80 CTC IDC type connector at the moment I do not know yet where to use. It 'a Quartz (near U96) and an additional IC LS04 (near U97) to generate the new clock frequency of the system is 6 MHz EPROM type 2732 and are now Dram IC type 4164 (there are present only 8).
There is no part of the circuit on the RS-232 interfaces, therefore, in addition to the components Z80 SIO / 0 and I / O 1488 and 1489 are not present U107 = 8116 and related quartz for synchronous serial transmission. It is also not present U95 = LS86. Finally, the power connector is 6 screws instead of 8. Has diskettes operating system CP / M file without the INIT and SYSGEN so you can have the disks only through their creation from file image with IMD.

Further tests showed that:

- When switching the contents of the 2732 EPROM is only partially copied into RAM at the address F800H;

- When booting the operating system, the loader shall copy the content in SD 182byte of the components of the CP / M (CCP BDOS and CBIOS) in RAM at the address 1000H, followed by the NEW firmware. Immediately after all, it is automatically copied from the address DC00H including the overlap of the new firmware in place of the original address F800H.

- The operating system is contained in a floppy disk with the following sequence: Track0-Side0 sect2-to-Track0 Side0-Sect26 + Track0 Side1-sect1-to-Track0 Side1-Sect26 + Track1 Track1-Side0-sect1-to-Side0 Sect12.

- Interesting maps the disks in CBIOS:
Drive0 = A = B and Drive1: volume data area DS / DD 1024byte from 9 sectors per track
Drive2 = C (A) and Drive3 = D (B): area data volume SS / SD 26 128byte sectors per track
Therefore, with the command: PIP A: = C *. *, You can copy files from C format SSSD 26 128byte sectors to A DSDD in size from 9 to 1024byte sectors.

MK83 ver. C (only wiring diagrams): In addition to the modifications introduced in version A, to implement a higher storage capacity drives has been added WD1793 chip with external data separator FDC9226B and related JB10 jumpers to set the delay on the precompensation in writing. Other changes are: U97 = ls06; U99 = LS243; U100 = LS243; Z80 all kind?; eprom 2716; Dram 4164.

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