[sdiy] Ursa major UART: WD2123

[MTG]

I see this a lot in CPU designs that won't boot with an LCD disconnected 
or bad. They stall in a polling loop waiting for the Busy Flag and since 
the LCD is disconnected or bad, they stall. A timeout is a much better 
coding practice. I wonder if there a similar thing going on here.

Does it boot if you simply pull the WD2123? Not sure what it would be 
waiting on for sure, but there might be a way of fooling the CPU into 
thinking it's there (like with a latch chip or something).

GB

On 10/26/2016 9:05 AM, Rutger Vlek wrote:
> Thanks for all the replies!
>
> The use of the WD2123 in the Ursa Major is fairly strange, as it is intended for connection of an (optional) external remote through an RS232 driver and connector. However, the Ursa Major won't start it's CPU properly if the communication with the UART can't be established. Kind of strange to be so dependent on something that's largely intended for "an option". I followed all suggestions in the service manual for debugging the CPU step by step and I have reached the step that says: "swap the WD2123 out for a known working one". Also, from common sense I don't see how CPU startup could otherwise be halted. Even a faulty RS232 driver should not break communication between the CPU and the UART, but merely lead to bogus input data from a non-existant remote controller.
>
> So my hopes are that a new WD2123 will get the CPU fully started again, as I'm out of alternatives.
>
> Rutger
>
>
>