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Information in this article applies to:

  • ISD51 Version 1.00
  • µVision2 Version 2.30
  • C51 Version 7.00
  • Keil MCBx51 Board with P89C664 PLCC 44 PIN


I am using the MCBx51 board with the PLCC44 Pin P89C664 and a 12MHz cystal. I use the Keil provided example GENERIC_8052 for the ISD51 single chip target debugger. I expect to connect to the board with a baud rate of 19230 based on the documented code. The actual baud rate to connect must be twice the baud rate (38460) for my board to connect. How could this be?


The baudrate for the Keil example GENERIC_8052 for the P89C664 at 12MHz (19230) and 24MHZ (38460) is with X2 Mode = 1 (ON) . Therefore, the P89C664 in your MCBx51 evaluation board must have been programmed for X1 or standard 8052 Mode. You would then have to connect at twice the baud rate in X1 mode as in X2 mode for this given example.

This example will be corrected in future releases to properly reflect the true meaning of GENERIC 8052 which would be in the standard or X1 Mode.

The reason for this was simply that most Philips chips are programmed in the X2 mode from the factory as the default. Many times you will need a parallel programmer to change the mode from X2 to X1 for the Philips chips.



Last Reviewed: Saturday, April 22, 2006

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