Richard,

The '420 is indeed a fast part. However only some opcodes execute single cycle. These are mostly the Accum/Reg instructions such as "ADDC A, Rn". So the 8051 architecture is starting to adhere to std. microprocessor "keep your work in the registers" requirement.

If you code "ADD A, direct" you will spend two cycles, If you code "MOVC A,@A+DPTR" you will spend three cycles. Interestingly the Multiply and Divide instructions are asymetrical coming in at 9 and 10 cycles respectively.

Now if you execute @ 11.0592MHz a single cycle costs ~90ns, with the Divide costing 904ns.

As you indicated that 11.0592 xtal could be internally multiplied and timing picks up in a hurry. Unfortunately, Dallas is currently only shipping parts that run at a max. of 33MHz so you could only mult. by 2 (there is no mult by 3).

The DPTR pointers are very well handled with new auto-inc instructions that would speed block operations quite a bit.

I am using this part now and like it a great deal.

regards,
p