Zilog Z08470 - Manual (Page 34)

Hardware and Software Implementation UM008007-0715
22
Z80 CPU
User Manual
Because the Z80 CPU requires only a single 5 V power supply, most small systems can be
implemented using only this single supply.
The external memory can be any mixture of standard RAM, ROM, or PROM. In Fig-
ure 18, a single 8 Kb (1 KB) ROM comprises the entire memory system. The Z80 internal
register configuration contains sufficient read/write storage, requiring no external RAM
memory.
I/O circuits allow computer systems to interface with the external devices. In Figure 18,
the output is an 8-bit control vector and the input is an 8-bit status word. The input data
can be gated to the data bus using any standard three-state driver while the output data can
be latched with any type of standard TTL latch. A Z80 PIO serves as the I/O circuit. This
single circuit attaches to the data bus as indicated and provides the required 16 bits of
TTL-compatible I/O. Refer to the
Z80 CPU Peripherals User Manual (UM0081) to learn
more about the operation of this circuit. This powerful computer is built with only three
LSI circuits, a simple oscillator, and a single 5V power supply.
Adding RAM
Most computer systems require some external read/write memory for data storage and
stack implementation. Figure 19 shows how 256 bytes of static memory are added to the
example shown in Figure 18.
The memory space is assumed to be organized as shown in Figure 20.
Figure 19. ROM and RAM Implementation
CE1
CE2
ROM
1K x 8
MREQ • RD
A
10
A
7
–A
0
D
7
–D
0
WR
RD
R/W
OD
CE2
A
10
A
7
–A
0
D
3
–D
0
CE1
WR
RD
R/W
OD
MRQ
Data Bus
D
7
–D
4
Address Bus
A
7
–A
0
RAM
256 x 4
RAM
256 x 4
A
10
MRQ
CE2
CE1