Top left edge of 510 board, mounted, as seen from front

     ____   ____________
 ___|    |_|            |____________________________
|    1  1   1 AX CONN  1                           B |
|    3  6              2                           U | 
|                                                  S |

The reset/console connector is designated "AX" in the OSI 510 schematics.

Connector pinout:

1   NC
2   Reset Switch GND
3   Reset Switch 
4   NC
5   NC
6   RS-232 GND
7   RS-232 TX
8   RS-232 RX
9   20 mA TX+ (+5V loop supply)
10  20 mA RX+
11  20 mA TX-
12  20 mA RX- (-9V loop supply)

The little 4-pin connector is also counted as part of the AX connector. Its
function relates to triple-processor selection. From the 510 schematics, it
looks like it can be used for either an external switch (pull lines to ground)
or to drive (buffered) indicators to show the active CPU under software 
control:

13	GND
14	/PSa (6502)
15	/PSb (6800)
16	/PSc (Z-80)

ROMs are located as such:

6502 ROMs:

  __  __  __  __  __  __  __  __
 |  \/  ||  \/  ||  \/  ||  \/  |
 | FD00 || FE00 || FF00 ||      |
 |      ||      ||      ||      |
 | HD   || 65A  || BOOT || 6502 |
 |      ||      ||      ||      |
 |______||______||______||      |
                         |      |
                         |      |
                         |      |
                         |______|

The 6800 ROM is the first 24-pin socket to the left of the Motorola 6800. It's
at 0xFF00 when the 6800 is switched in.

The boot ROM in my 510 board (located at 0xFF00) does the initialization of the
system and floppy boot. It's what is responsible for the "H/D/M?" prompt. How
it works:

    * Jump to 0xFD00 if you select 'H' (hard disk boot)
    * Jump to 0xFF00 if you select 'D' (floppy boot)
    * Jump to the address located at 0xFEFC for anything else

0xFEFC is the "reset vector" in the 65A ROM monitor. On my version of the 65A
monitor, this points to 0xFE35.