Building information for the Re-UD-80 board

Power supply

The board is prepared for the classic 9V DC wall-brick, supplied through a barrel-jack 2.1/5.5mm with pin positive. The regulator has the same pin-out as the LM7805. There is little room for a cooling sink,  so a switching regulator is advised.
On the other hand, power consumption is modest, ~200mA, so it is feasible to power the board directly from a USB charger or power bank. Do not solder a 7805 and short its input solder pad to the output pad and directly connect 5V to the barrel-jack socket. This works quite well. I have yet to add a regulator to a board.

Connectors

See the oval80replicaV0.10.connectors.pdf file (files section) for more info on what connector or jumper should do.

List of unstructured information and observations:

• The Re-UD-80 can use both 2k and 8k Byte Static RAM, as this was a jumper option for the UD-80. I am not sure the extra 6 k Byte is actually used. This is jumper J1 on the replica.
• The Re-UD-80 can accommodate 27128 and 27256 EPROMs, or the CMOS versions of those. The address range remains 16 kByte, but a larger 27256 can be used to switch between two firmware versions. This is jumper J8.
•  The RGB video DIN-part is used for color displays. The RCA plug carries a gray-level signal. I have yet to see an indication that color is actually used. Other color-only components: R18 to R22 and C24.
• The ROM is in the upper half of the memory space of the 6803, it uses it's internal RAM for housekeeping. The RAM is only accessible by the EF9345. The eight registers of the EF9345 fill most of the lower half of 6803 memory (excluding space reserved for internal RAM and registers).
• When the ROM isn't seen by the 6803, the serial LEDs can blink rhythmically. During normal operations they are off. One blink when the Filink switch is pressed, and more during Filink transfer and normal access.
• When the RAM isn't seen by the EF9345, a video signal is generated, but filled with random characters.
• The R, G  and B channels for the gray-level output have different series resistors, which should allow for eight different gray-levels.
• The 74LS08 can be replaced by a 74LS32. Not because AND is the same as OR, but all the gates are used as buffers, and the pinout is the same.
• The top line of the screen is reserved by the banner:
  Oval UD-80+ Display Controller V5.21E
  or
  Oval UD-80A++ Video Controller V7.11c
• When you want to test the Re-UD-80 without having the cable to the PX-8 or PX-4, you can connect it to a PC and send characters to the serial to which it is connected; 4800Bd, 8 bits, no parity.
• When you cannot find a cheap MC6803 or HD6303, an MC6801 will also work. The 6803 is a limited mode version of the 6801, but capable of the mode used in the Re-UD-80.