kenwillmott / hd6303evb Goto Github PK

MR signal extends E signal time. It can be tapped from the 02 output of U6B decoder, then all memory accesses from C000-D000 in the bus address range will be slower. Some legacy parts are not fast enough for 2MHz bus speeds so it should be an on board jumper option.

The spacing between adjacent bus connectors is too small. The right angle connectors that are planned for the peripheral cards require a wider gap. The dimension needs to be estimated.

Both 16k banks of the NVRAM are selectable via a jumper. That choice should be addressable in software. To do that, the Vcc pin of the jumper should instead be connected to some I/O pin configured for output.

Currently the power comes from the USB-serial adapter. For more flexibility, a dedicated power supply connector and a jumper to select either it, or the USB power should be added.

The pin header through holes are on 2mm centres and so don't align with the 2.54mm centres on a typical pin header. Fix in next revision.

No issue, just to help.

Several devices utilize the RESET line, connected to an RC circuit. This means devices come out of reset at different times because the reset circuit signal is very slow, and inputs have different logic thresholds. It may be better to buffer the reset signal so that all devices are reset simultaneously.