SX28 strange problem

Zamuel

I have just started to experiment with the SX28 and I'm doing a project there I have a signal that is sent from a computer and I want to detect it with the SX28 so I made a poll loop for that pin (one of the RA pins) and it works if the frequency of the oscillator is low. If I run upto about 30MHz it seems to work, but if I connect a higher frequency oscillator it nearly never works. It's like it miss the input signal. Sometimes it works, sometimes not. First I thought it was the input signal that was to fast so I had to go up in frequency but the signal is about 200ns long so it should be plenty of time and the problem seems to be the opposite to what I thought! I need to go down in speed! I have tried most of the settings. SYNC/NO SYNC, INPUT PULL UP, CMOS/TTL inputs and I have the clock defined as HS3
I'm using the Parallax SX28AC

JonnyMac

Seeing a schematic of the connection and the code you're using would help others help you.

Zamuel

Here is the code. I'm just waiting for a signal to go low on RA pin 3 and it works if the clock is lower then around 30MHz


··DEVICE··SX28,OSCHS3,TURBO

IFDEF·__SASM· ;SASM Directives
··DEVICE··STACKX,OPTIONX
··IRC_CAL··IRC_SLOW

ELSE··;Parallax Assembler Directives
··DEVICE··STACKX_OPTIONX
ENDIF

··RESET··Initialize

;

---

DEBUG SETTINGS

---

··FREQ·70_000_000

;

---

INITIALIZATION ROUTINE

---

initialize

·mode·$0F ··;Set Mode to allow Direction configuration
·mov·!RA,#%1100 ·;Port A bits 0-1 to output, rest inputs
·mov·RA,#%1110

main

wait·jb·RA.3,wait
·jmp·start

start·clrb·RA.1
·jmp·start

Zamuel

I think I solved the problem now! I had an external 14pin DIL oscillator connected to the SX directly and then I looked on the frequency signal with a scope it looked alittle strange. Like a sinus wave and with an amplitude of around 12Volt, even that I only have 5V connected, so I put a inverter from a 74HC04 IC between the oscillator and the SX to "clean up" the signal and after that it works!