DS80C320-MCG Datasheet, PDF (70/175 Pages) Dallas Semiconductor – High-Speed Microcontroller User Guide

High-Speed Microcontroller User’s Guide
Note that in the first example, the first memory access is the opcode. The second memory access is the
location of the operand in the register map. Since the result is stored in an internal register, this operation
does not require a memory access. The second example is very similar. Again, the first byte represents
the opcode. In this example, the second byte is the operand itself. This byte is used directly by the
instruction. The timing for a two cycle instruction is shown in Figure 5-4.
One other type of two cycle instruction requires two cycles but only includes one byte. This is because
the second memory access is the result of the instruction. These are the MOVX instructions. An example
is as follows:
MOVX
@DPTR,A F0h
The second cycle in this instruction is the write to data memory at the address pointed to by the data
pointer. Thus this instruction is a two cycle one byte instruction, but requires two memory accesses. The
MOVX timing is a special case, since the user can control it with the Stretch MOVX feature. The timing
for the Stretch MOVX is discussed in the section on Memory Access.
SINGLE CYCLE INSTRUCTION TIMING Figure 5-3
C1
CLK
SINGLE CYCLE
C2
C3
C4
ALE
PSEN
AD0-7
PORT2
RETURN DATA
D7-0
ADDRESS A15-A8
*Shaded areas are held in a weak latch on the port until overdriven.
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