Zilog Z08470 Manuel d'utilisateur télécharger pdf (Page 202)

UM008101-0601 Parallel Input/Output

IEI

Interrupt Enable In (input, active High). This signal is used to form a

priority interrupt daisy-chain when more than one interrupt driven device is

being used. A high level on this pin indicates that no other devices of higher

priority are being serviced by a CPU interrupt service routine.

IEO

Interrupt Enable Out (output, active High). The IEO signal is the other

signal required to form a daisy-chain priority scheme. It is High only if IEI

is High and the CPU is not servicing an interrupt from this PIO. Thus, this

signal blocks lower priority devices from interrupting while a higher

priority device is being serviced by its CPU interrupt service routine.

INT

Interrupt Request (output, open-drain, active Low). When INT is active,

the Z80 PIO is requesting an interrupt from the Z80 CPU.

A7-A0

Port A Bus (bidirectional, tristate). This 8-bit bus is used to transfer data

and/or status or control information between Port A of the Z80 PIO and a

peripheral device. A0 is the least-significant bit of the Port A data bus.

ASTB

Port A Strobe Pulse from Peripheral Device (input, active Low). The

meaning of this signal depends on the mode of operation selected for Port A

as follows:

1. Output mode: The positive edge of this strobe is issued by the peripheral

to acknowledge the receipt of data made available by the PIO.

2. Input mode: The strobe is issued by the peripheral to load data from

the peripheral into the Port A input register. Data is loaded into the

PIO when this signal is active.

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Zilog Z08470 Manuel d'utilisateur Page 202