C.2 Serout on 28X2....

Hi folks.

Replacing an original 28X chip with a 28X2 chip, cos the original blew up in a lightning strike.

4MHz extremal resonator as per the 28X chip. 5v supply voltage.

Replacement X2 part programs fine, and runs fine, but the serial output won't go through a 202 level corrector - does anyone know if there should be anything different between the 28X and 28X2 parts that would stop that?

If I remove the 202 chip and tap directly into the serial from the 28X2 with a terminal program, I am getting the expected output, so the data is coming out of C.2 OK, but it won't pass through the level corrector.

I'm a bit stumped about this at the moment, cos it should just work if it is coming out of the X2 OK, but when you plug the output from the 202 into a laptop or anything else, all I get is garbage on the screen, not the wanted data.

Anyone got any ideas?

The 4MHz resonator will cause the 28X2 to run at 16MHz if it is 'engaged' with a SetFreq EMxx command (regardless of the xx value that you specify).

You can run the 28X2 at 4MHz on its internal resonator.

The default speed of the 28X2 is 8MHz. All of these different speeds will affect the baud rate of serial data.

Excellent point, thanks. I will remove the 4MHz resonator and see if things behave then. Everything worked fine before the strike, but that was the older 5v 28X part, not the newer X2 part, so yeah - resonator - never thought of that..... Will keep the thread updated. Thanks for the reply.

You can leave the resonator in place; removing it will not solve a baud rate issue caused by the 28X2 running at a faster speed than the 28X did.

FIXED. I discovered that the laptop I was using seems to have a crook serial port. That was unexpected, but when I connected the RS232 output from the MAX202 via a longer cable to my big PC, it was showing up there just fine, but plug the same cable into the laptop, and it is garbled. TeraTerm on both machines, both set to 4800 baud 8N1, but TT on the PC worked fine, laptop just shows garbage. Looks like it was THAT throwing me. Curses. However, all seems to be working OK again now. Stupid lightning strike. So many faults in different systems all at the same time. Very easy to get confused if you don't watch it. I will test this laptop with some other serial things to be sure, but it's an old Pentium2 with Windows 98 on it, so..... I only kept it for it's native serial port, but with USB-serial adaptors being very reliable nowadays.....