7-bit (7/1/E) w/Schenk's FDS?

luftphoto

I've hit a brick wall here. Help!

Almost a year ago I posted about a small project I was working on that would need 7-bit serial comm capability. Somewhere along the way someone gave me, or I somehow found a modified version of "full duplex serial", modified by Andy Schenk (and can be downloaded here: http://forums.parallax.com/forums/attach.aspx?a=29977 ).

The modded version of FDS works great for transmit but no matter what I try I can't force it to receive 7-bits, even forcing it to ignore parity, etc... I use this .spin for output and it's absolutely perfect so I'd like to just hack the receive code if possible. Any ideas?

Ariba

Hello luftphoto

If you have 7 bits with Even parity, then these are 8 bits total. On transmit the driver can replace the highest bit with the right parity. On receive the highest bit representate the parity that the sender on the other side sends, but this bit is not checked against correctness.
So you get 8 bits bit 6..0 = 7bit Data, bit 7 = parity. If you don't want check the parity, then you can ignore it with:

data := <obj>.rx & %01111111

This masks bit 6..0 and set bit 7 to zero. <obj> is the name of your included serial object.

Andy

luftphoto

Andy, thanks! I was heading in that direction but was concentrating on the assembly part of the code, it worked fine.

If anyone else needs the info, I changed the code here:

PUB rxcheck : rxbyte

'' Check if byte received (never waits)
'' returns -1 if no byte received, $00..$FF if byte

rxbyte--
if rx_tail <> rx_head
rxbyte := rx_buffer[noparse][[/noparse]rx_tail] & %01111111
rx_tail := (rx_tail + 1) & constant(RXBUFFSZ-1)

gpost

I am looking for a serial object that can handle 7 bit, 1 start, 1 stop, even parity.

@luftphoto: Care to post your complete code? (can't seem to follow original link)

Ariba

I have attached it.

But the object sends 2 stop bits, I hope this is not a problem.

Andy

gpost

Thanks for the code Ariba. I will see if I can figure out how modify the code for 1 start bit and 1 stop bit. A bit of a daunting task since it's been 7 years since I have looked at anything that resembles assembly