C51: BITS USED FOR BANK SELECTION

QUESTION

I want to use bits 2 and 7 of port 1 for bank selection. Is the C51 toolset able to do this?

ANSWER

You can't easily do this as the bits are required to be consecutive. Although the explicit statement is not in the book, these bits must be allocated sequentially. If you specify ?B_FIRST_BIT is bit 3 and ?B_PORT is P1 and the number of banks is 32, then the pin allocation for bank selection would be:

P1.3
P1.4
P1.5
P1.6
P1.7

There is no provision for gaps of any kind in the pin allocation. This is true for both I/O ports and XDATA latches.

Since the source code is provided for the bank selection algorithms, you may write your own code to support this, however, that will be more work on your part.

Last Reviewed: Saturday, May 08, 2004