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UM008101-0601 Serial Input/Output

210

PIN DESCRIPTION

Pin Functions

D7-D0 System Data Bus (bidirectional, tristate). The system data bus

transfers data and commands between the CPU and the Z80 SIO. D0 is

the least-significant bit.

B/A

Channel A or B Select (input, High selects Channel B). This input

defines which channel is accessed during a data transfer between the CPU

and the Z80 SIO. Address bit A0 from the CPU is often used for the selec-

tion function.

C/D

Control Or Data Select (input, High selects Control). This input

defines the type of information transfer performed between the CPU and

the Z80 SIO. A High at this input during a CPU write to the Z80 SIO

causes the information on the data bus to be interpreted as a command for

the channel selected by B/A

.ALowatC/Dindicates that the information

on the data bus is data. Address bit A1 is often used for this function.

Chip Enable (input, active Low). A Low level at this input enables the

Z80 SIO to accept command or data inputs from the CPU during a write

cycle, or to transmit data to the CPU during a read cycle.

Φ System Clock (input). The Z80 SIO uses the standard Z80A System

Clock to synchronize internal signals. This is a single-phase clock.

Machine Cycle One (input from Z80 CPU, active Low). When M1 is

active and RD

is also active, the Z80 CPU is fetching an instruction from

memory; when M1 is active while IORQ is active, the Z80 SIO accepts

and IORQ as an interrupt acknowledge if the Z80 SIO is the highest

priority device that has interrupted the Z80 CPU.

IORQ

input/Output Request (input from CPU, active Low). IORQ is used

in conjunction with B/A,C/D,CE,andRDto transfer commands and data

between the CPU and the Z80 SIO. When CE

,RD,andIORQare all active,

the channel selected by B/A

transfers data to the CPU (a read operation).

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Zilog Z08470 Manual de usuario Pagina 230