I have been working on my AT89Cx051 programming board, and a couple of questions have come up... I guess some of you here have some experience programming these (or other) chips.

First a short description of my board. P1 of the AT89Cx051 is connected to P1 of the 80c31 chip that's supposed to handle the programming. P3 (on the AT89Cx051) is connected to a 574 latch through a 07 buffer. The output of the buffer is pulled high through 4k7 resistors.

And now the questions:

What state should the various pins be in while the AT89Cx051 chip is inserted (or removed)? Vcc and Vpp (RST) are both at 0V, but what about the P1/P3 pins? Should they by pulled down or left floating (high)? If they float the Vcc LED lights dimly, so it looks like the chip draws current throgh the pull-up resistors.

Is the XTAL1 pin (used to increment the address counter) supposed to draw current? When I set the XTAL1 pin high (controlled by a P3 pin on the 80c31), it doesn't get very high... I tried adding a 4k7 pullup, but it still only reaches 2.6V. According to the datasheet 3.5V is needed. I guess I have a bad chip, or that my experiments killed it - but of course I don't have any other chips for verifying... ;-)

When I read the signature bytes the first one is ok (0x1e). The second byte is read as either 21, 23 or 255, but I guess that's caused by the XTAL1 problem mentioned above. I'll include the code I use for reading the signature bytes below, just in case someone hasn't got better things to do than read bad code ;-) If anyone spots errors I might as well fix them before I destroy more chips...

Best regards,

Mikkel C. Simonsen

//Power-up sequence
//Set port 1 high
P1 = 0xff;
//Apply power (Vcc+Vpp)
portb = 0x4;
//Set RST and XTAL1 to GND
portb = 0x7;
DXTAL1 = 0;
//Set RST to H
portb = 0x4;
//Set P3.2 to H
DP32 = 1;

//Read signature byte
_nop_();
c = P1;
uln(10);
if (c == 0x1e) strcpy(chvendor, "Atmel");
else
	{
	strcpy(chvendor, "unknown ");
	sprintf(str, "%i", (int)c);
	strcat(chvendor, str);
	}
udskrivs("                        The chip is an ");
udskrivs(chvendor);
udskrivs(" ");

//Increment address counter
DXTAL1 = 1;
_nop_();
pause(1);
DXTAL1 = 0;
_nop_();

//Read signature byte
c = P1;
if (c == 0x41)
	{
	strcpy(chtype, "AT89C4051");
	chsize = 4096;
	}
else if (c == 0x21)
	{
	strcpy(chtype, "AT89C2051");
	chsize = 2048;
	}
else if (c == 0x12)
	{
	strcpy(chtype, "AT89C1051U");
	chsize = 1024;
	}
else if (c == 0x11)
	{
	strcpy(chtype, "AT89C1051");
	chsize = 1024;
	}
else
	{
	strcpy(chtype, "unknown ");
	sprintf(str, "%i", (int)c);
	strcat(chtype, str);
	chsize = 4096;
	}
udskrivs(chtype);
udskrivs("rn");

//Power down sequence
//Set XTAL1 to L
DXTAL1 = 0;
//Set RST to L
portb = 0x7;
//Turn Vcc power off
portb = 0x47;
//Set port 1 low
P1 = 0x00;
DP31 = 0;
DP32 = 0;

udskrivs("nn   * * * Press any key to continue * * *");

uln(11);

while (! RI);
c = SBUF;
RI = 0;