Consumer Electronics

THE Z80 AND THE 8051

The Z80 (Table 48.1) has a very rich instruction set. The penalty that is paid for this abundance is the number of multi byte instructions needed, some 71% of the total number. Each byte of a multibyte instruction must be fetched from program memory and each fetch takes time, this results in longer program byte counts and slower execution time versus single byte instructions. The 8051 has a 62% multi byte instuction content; the 8051 program is more compact and will run faster to accomplish similar tasks.

The disadvantage of using a lean instruction set, as in the 8051, is increased programmer effort (expense) to write code; this disadvantage can be overcome when writing large programs by the use of high-level languages such ...