Figure 15. typical cpu i/o sequence – Zilog Z08470 User Manual
Page 52
< %27 2GTKRJGTCNU
7UGT /CPWCN
UM008101-0601
Direct Memory Access
Figure 15.
Typical CPU I/O Sequence
The Z80 and Z8000 CPUs both have block-transfer and string-search
instructions that can operate on up to 64 Kbytes of data with a single
instruction.
A single block transfer instruction repetitively performs all of the functions
illustrated in Figure 15 on an entire sequence of bytes. Therefore, transfer
rates are significantly faster. The 4 MHz Z80A CPU can transfer at about
200 Kbytes/sec and the 4 MHz Z8000 CPU can reach 800 Kbytes/sec.
The problem with CPU block transfers in the Z80 and Z8000 devices is not
transfer speed but response time at startup. One of the following methods is
normally used to set up executing a block transfer instruction:
Read
Source Port
Write to
Destination Port
Increment
Address Counter
Increment
Byte Counter
NO
YES
END
Byte Count
Equal
Block Length
?