1. Может в каких-то версиях Z80 этот cчётчик 8 битный? (Z80A, Z80B, ...)
2. Можно ли в регистр R прописывать значения >= 128 ?
3. Какой смысл анализировать старший бит этого регистра, если он не меняется (или нулевой) ? Я это вижу в проге.
Для стандартного Z80 есть такое описание.
Цитата
The refresh register, R, increments each time the CPU fetches an opcode (or opcode prefix) and has therefore no simple relationship with program execution.
["While R is an 8 bit register, it wraps around at 128 instead of 256. If the programmer stores a value in the register, its high bit will be preserved regardless of what the CPU does to the remaining 7 bits. Incorrect implementation of this behaviour is a common source of problems when running games on emulated Z80-machines"]
["While R is an 8 bit register, it wraps around at 128 instead of 256. If the programmer stores a value in the register, its high bit will be preserved regardless of what the CPU does to the remaining 7 bits. Incorrect implementation of this behaviour is a common source of problems when running games on emulated Z80-machines"]
На 2-ой вопрос ответ ясен.
