Exploring the serial I/O of a 40+ year old uP / MPU / SBC / TTL device

@ser156811

First, thank you for reading thru and sharing your thoughts.

Regarding speed, I had a similar thought: can Espruino Pico - the serial appliance of the STM32F401CDU6 - go so low down to 300 bps, but did not think about the divider issue... I should though have taken that though serious, since I know how USARTs (chips of same age) have to be configured...

I also had the thought of using Espruino firmware's software serial... but it may have the very same issue. After all, it uses the same basic hardware: some timer(s), relaying on the same counters...

There are server options for a next step before more serious actions have to be considered:

1. Change Serial1 to a software new Serial()... very easy to do
   
2. The device has also an output only serial routine using similar bitbanging hardware and software, but with configurable baud rate, and it usually ran on 1200bps and can go up to 400bps. Disadvantages are: has no parity, no CRC (checksum), and disabling for full control of the device: it has output ONLY. The input is only for checking DTR.
   
3. Making changes to the firmware of the device, posing several sub-options. The devices hardware is though too weak for a reasonable implementation of a configurable, bidirectional serial communication to implement serial with XON/XOFF flow control. Basically: there is no independent time or interrupt control used (and implemented in the devices monitor).
   
   

Hooking on a scope is an option... which I did 40+ years ago when validating the devices capabilities and putting it to service. Time fluctuations according to Espruino Poco's measurments are at it's most extreme in the range of 0.003152 thru 0.003157 (time of 1 bit), which is less than 0.2%. With that, I can comfortably exclude accuracy issues, but for sure not speed range ones.

New results will be available soon.