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ST7 AND ST9 PERFORMANCE BENCHMARKING

4.3 MEDIUM-END TO LOW-END MCU ANALYSIS VERSUS ST7

The Table 4 presents the strong and the weak points for medium-end to low-end MCUs,

compared to the ST7 MCU.

Notes: ICT means Instruction Cycle Time and IL means Instruction Length.

Refer to paragraph <Italic>7.2.2 Average ICT/CPI and IL<Italic end> for details on

calculation.

Refer to paragraph <Italic>7.3.9 ST7 MCU core<Italic end> to see the main characteristics of

the ST7 MCU core.

4.3.1 Computing performance results

Regarding speed, the ST7 MCU takes the second position just below the newly arrived

68HC08. With no prefetch mechanism, it comes even so ahead of all the other MCUs. A short

clock per instruction added to a standard frequency explains its short instruction cycle time

and its advantageous position. The two index registers and the indirect addressing mode

allow the ST7 to easily perform data manipulation like table manipulation and block move.

A direct addressing mode in a 256-byte zero page give a rapid access to important data

and peripheral registers.

Concerning code efficiency, the ST7 MCU ranks among the 8-bit MCUs, very closely above

the 68HC08. A standard instruction length explains its average position.

4.3.2 Interrupt processing performance results

Regarding speed, the ST7 MCU ranks very close to the 68HC08. A longer instruction cycle

time explains this tiny gap. The strong point of its interrupt management is the automatic

stacking of the cpu state, accumulator and index register. This process eliminates software

stacking, and so saves time and space.

Code efficiency results for interrupt processing performance are not really significant. The

code represents only a very small part of an entire interrupt service routine, and so no

conclusion can be made.

4.3.3 Conclusion

Global results and all its characteristics confirm the ST7 as an outstanding 8-bit MCU.

AN910 Datasheet(PDF) 15 Page - STMicroelectronics