Something rather odd with background serial receive on a 20X2.
I'm driving the HSERIN pin (aka B.6) from the output of a 74F00 logic gate, that itself receives the serial signal from an opto-isolator.
If I connect the gate output directly to HSERIN, then I get wildly inaccurate serial reads - it seems to mis-read 10% to 40% of the received characters.
If I put a 4.7K resistor between the gate and HSERIN, the accuracy greatly improves to pretty much 100%.
I can't find any logical reason why I'd need to do this, but it really does influence the read accuracy. I stumbled upon it by accident (accidentally connected the gate through the same resistor circuit - 22K and 10K to ground - normally used with a direct PC serial connection when I didn't mean to, but noticed that the inaccuracy disappeared when I did this; then I progressively whittled it down to the single 4.7K resistor).
Why would this be so?
I'm driving the HSERIN pin (aka B.6) from the output of a 74F00 logic gate, that itself receives the serial signal from an opto-isolator.
If I connect the gate output directly to HSERIN, then I get wildly inaccurate serial reads - it seems to mis-read 10% to 40% of the received characters.
If I put a 4.7K resistor between the gate and HSERIN, the accuracy greatly improves to pretty much 100%.
I can't find any logical reason why I'd need to do this, but it really does influence the read accuracy. I stumbled upon it by accident (accidentally connected the gate through the same resistor circuit - 22K and 10K to ground - normally used with a direct PC serial connection when I didn't mean to, but noticed that the inaccuracy disappeared when I did this; then I progressively whittled it down to the single 4.7K resistor).
Why would this be so?