Owner's manual

5-16
Ultra-High-Speed Flash
Microcontroller User’s Guide
Comparison to the 8051
The original 8051 needed 12 clocks per machine cycle and most instructions executed in either one or two machine cycles. Thus,
except for the MUL and DIV instructions, the 8051 used either 12 or 24 clocks for each instruction. Furthermore, each machine cycle
in the 8051 used two memory fetches. In many cases the second fetch was a dummy, and the extra clock cycles were wasted.
The ultra-high-speed microcontroller uses one clock per memory (or machine) cycle. Where there were primarily one- and two-cycle
instructions before, an instruction on the ultra-high-speed microcontroller may take between one and ten cycles. The divide instruction,
for example, requires 10 cycles. Note however, that the 10 cycles needed for the DIV AB instruction can be executed at one clock per
cycle (10 x 1 = 10 total clock cycles). The instruction is executed 4.8 times faster than the original 8051 architecture which required
four cycles at a rate of 12 clocks per cycle (4 x 12 = 48 total clock cycles). Each instruction is at least four times faster, with the high-
est throughput improvement being 24 times that of the original 8051 architecture.
Table 5-1 shows each instruction, the number of clocks used in the ultra-high-speed microcontroller, and the number used in the 8051 for
comparison. The factor by which the ultra-high-speed microcontroller improves on the 8051 is shown as the speed advantage. A speed
advantage of 12 means that the ultra-high-speed microcontroller performs the same instruction 12 times faster than the original 8051.
Table 5-2 provides a summary by instruction type. Note that many of the instructions provide multiple op codes. As an example, the
ADD A, Rn instruction can act on one of eight working registers. There are eight op codes for this instruction because it can be used
on eight independent locations. Table 5-2 shows totals for both number of instructions and number of op codes. Averages are provid-
ed in the tables. However, the real speed improvement seen in any system depends on the instruction mix.
Table 5-1. Instruction Timing Comparison
Ultra-high-speed microcontroller is abbreviated as UHSM.
INSTRUC TION HEX CO DE
U HS M CLOC K
CYC LES
U HS M TI ME @
25MHz
8051 CLOCK
CYC LES
8051 TIME @
25MHz
U HS M vs. 8051
SPEED
A DVA N T AGE
ADD A, Rn 28..2F 1 40 ns 12 480 ns 12
ADD A, direct 25 2 80 ns 12 480 ns 6
ADD A, @Ri 26..27 2 80 ns 12 480 ns 6
ADD A, #data 24 2 80 ns 12 480 ns 6
ADD C A, Rn 38..3F 1 40 ns 12 480 ns 12
ADD C A, direct 35 2 80 ns 12 480 ns 6
ADD C A, @Ri 36..37 2 80 ns 12 480 ns 6
ADD C A, #data 34 2 80 ns 12 480 ns 6
SUBB A, Rn 98..9F 1 40 ns 12 480 ns 12
SUBB A, di rect 95 2 80 ns 12 480 ns 6
SUBB A, @Ri 96..97 2 80 ns 12 480 ns 6
SUBB A, #data 94 2 80 ns 12 480 ns 6
INC A 04 1 40 ns 12 480 ns 12
INC Rn 08..0F 1 40 ns 12 480 ns 12
INC di rect 05 2 80 ns 12 480 ns 6
INC @Ri 06..07 2 80 ns 12 480 ns 6
INC DPTR A3 1 40 ns 24 960 ns 24
D E C A 14 1 40 ns 12 480 ns 12
D E C Rn 18..1F 1 40 ns 12 480 ns 12
Maxim Integrated