I tried to collect information on the parts needed for SBC and there seems to be a problem with the reset IC suggested.
The parts list and schematics lists a 3-legged reset of Panasonic, MN13811. According to the datasheet, that is an open-drain, active low reset (see page 7) - hence, not suitable for common '51s. The active high TO-92 reset part is MN13812, however, it is push-pull.
I know why this happened: digikey lists them in this - erratic - way.

The problem with push-pull is, that the RESET line is connected also to both ISP circuits where it is driven by LS125/LS126 outputs. Even the open-drain reset is not perfectly kosher, but as most of the time reset via ISP would be activated only while there is full power on the board, there is perhaps little risk in it (maybe a series resistor would be enough to avoid deadly conflicts).

However, after really extensive search, I was unable to find a open-collector/drain active-high three-legged (TO-92) reset (digikey lists a Zetex part, ZSH560, but they have no stock and the Zetex site displays last-orders on last year, so it is obvious it is already obsolete).

Well but if we are left with active-high push-pull part (and for the ISP, manually switching to the RC-reset), it is probably better to use a Microchip MCP101 (D-bondout) - not only is it 60% cheaper, but it might be more readily available worldwide - I tried to locate it here but no success; also there is no trace of any reset circuit on Panasonic website, so they might have already obsoleted the MN13812. MAX810 would be perhaps better, as it is massively second-sourced; but it is in SOT23-3 only.

Comments?

Jan Waclawek