USB Serial Communication Continuous

[mister_e]

I've never tried with a DEFINE OSC 20... but i think it's the main problem.

Look how i did it in mine. (config fuse as well)

and now

DoLow:
LOW PORTC.0
USBSERVICE
PAUSE 30
USBSERVICE
return

This example don't use instant interrupt, inserting a PAUSE and using On INTERRUPT GOTO might cause some problem for the USBSERVICE.

next point...i don't know what's happen if you use both HSER_BAUD and HSER_SPBRG together... Assuming HSER_SPBRG may override the HSER_BAUD, you have a big problem as your SPBRG value is way out of range @20MHZ... but good @8MHZ.

to have 2400 baud @20MHZ, you should use...

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 20h ' Enable transmit, BRGH = 0
DEFINE HSER_SPBRG 129 ' 2400 Baud @ 20MHz, 0.17%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically

I do believe the HSER_CLROERR may help a little bit.

There's probably something else... i feel a bit lazy today

[pic-ker]

I've never tried with a DEFINE OSC 20... but i think it's the main problem.

Look how i did it in mine. (config fuse as well)

I have tried it with a DEFINE OSC 48 as well....infact the USB interface works fine...i tried to switch on/off the LED pins on you demo and they work ...

The config fuses are
24 0E 3E 00 00 83 81 00 0F C0 0F E0 0F 40

in either case (48 or 20)
i have defined the PLL and OSC setting in the .inc file so the DEFINE directive has no effect


in the case of :

DoLow:
LOW PORTC.0
USBSERVICE
PAUSE 30
USBSERVICE
return

i found that this code does work...and it does generate a delay of 30ms on the Oscilloscope without affecting the Tx USB connection....The TX seems to be transmitting fine...

[pic-ker]

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 20h ' Enable transmit, BRGH = 0
DEFINE HSER_SPBRG 129 ' 2400 Baud @ 20MHz, 0.17%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically

I do believe the HSER_CLROERR may help a little bit.

Thanks, I'll try that now...

[pic-ker]

I havre tried all the above statements....

DEFINE HSER_CLROERR 1 is now inculded...

however im still getting errors...
i transmit : 239 65 66 67
I receive : 254 254 6 134 128
(5 chars for tx of 4 chars)

maybe its because i used SEROUT in conjunction with HSERIN ?

[mister_e]

And... do you get always the same results or they are always different?

[pic-ker]

Differnet results each time...


Anyway I have finally got the TX/RX to work !

Heres the section of the TX code which works:

IF USBBufferIn[7]=239 then
SEROUT PORTC.0,T2400,[USBBUFFERIN[7]]
gosub DoLow
USBBufferin[7]=0

if USBBufferIn[1]<>0 then
SEROUT PORTC.0,T2400,[USBBufferIn[1]]
gosub DoLow
USBBufferIn[1]=0
endif
USBService
if USBBufferIn[2]<>0 then
SEROUT PORTC.0,T2400,[USBBufferIn[2]]
gosub DoLow
USBBufferIn[2]=0
endif
USBService
if USBBufferIn[3]<>0 then
SEROUT PORTC.0,T2400,[USBBufferIn[3]]
gosub DoLow
USBBufferin[3]=0
endif
USBService
if USBBufferIn[4]<>0 then
SEROUT PORTC.0,T2400,[USBBufferIn[4]]
gosub DoLow
USBBufferin[4]=0
endif
USBService
if USBBufferIn[5]<>0 then
SEROUT PORTC.0,T2400,[USBBufferIn[5]]
gosub DoLow
USBBufferin[5]=0
endif
USBService
if USBBufferIn[6]<>0 then
SEROUT PORTC.0,T2400,[USBBufferIn[6]]
gosub DoLow
USBBufferin[6]=0
endif
USBService
endif

gosub dousbin


goto start

DoLow:
USBSERVICE
PAUSE 65
USBSERVICE
return

Notes:
1. You need to use the T mode if you are directly connecting PIC's.
2. Notice the Pause 65 - It now works great with a longer delay...and has no effect on the USB connection.


Heres part of the modified RX code :

DEFINE HSER_CLROERR 1 ' Clear overflow automatically
Define HSER_RCSTA 90h
Define HSER_BAUD 2400

The oscillator is set to 20Mhz in both cases using : DEFINE OSC 20
__________________________________________________ _______________

Now that the wired link is working....I checked it using a FSK TX/RX pair
and the problems are endless....
Completely random characters etc
Characters appear when i move my hand in the air !
I have tried a passive Bandpass filter around 2400hz but it doesnt sove the problem...
I have connected a Schottky TTL gate to the DataOut...for maintaining proper level transitions...
Also when I connect a LED to the DataOut of the RX it keeps flickering at a fast rate (around 10kz on the oscilloscope),even when the Tx is off...which is probably whats causing the errors..

Any ideas on how to fix this ? or is the RF module faulty ?

[Dave]

pic-ker, I bet the RF receiver module you are trying to use has no squelch control and the toggling of the receiver output is the data slicer trying to interpret noise. You will have to put some kind of sync and preamble bytes in place before you transmit the data and, if the sync and preamble bytes are not received in order and correctly you should not accept the data. This is the common problem people have when using inexpensive rx and tx modules. Even with more expensive modules the same sync/preamble techniques should be used. Also you should send a computed checksum as the last byte and this checksum should be checked at the receiver end before using the data received.

Dave Purola,
N8NTA

[pic-ker]

pic-ker, I bet the RF receiver module you are trying to use has no squelch control and the toggling of the receiver output is the data slicer trying to interpret noise. You will have to put some kind of sync and preamble bytes in place before you transmit the data and, if the sync and preamble bytes are not received in order and correctly you should not accept the data. This is the common problem people have when using inexpensive rx and tx modules. Even with more expensive modules the same sync/preamble techniques should be used. Also you should send a computed checksum as the last byte and this checksum should be checked at the receiver end before using the data received.

Dave Purola,
N8NTA

Yeah, youre right, the module was really cheap ... it doesnt have a crystal based oscillator, rather there is an inductor coil which can be adjusted by a screwdriver....

I think it would be better if I get another module :-) instead of doing all that syncing/CRCing etc