Zilog Z08470 Manual de usuario descargar pdf (Pagina 209)

UM008101-0601 Parallel Input/Output

SelectingAnOperatingMode

PIO Port A allows operation in four modes: Mode 0 (output mode), Mode 1

(input mode), Mode 2 (bidirectional mode), and Mode 3 (control mode).

The mode numbers are assigned for mnemonic significance: 0 = Out,

1 = In, 2 = Bidirectional. Port B cannot operate in Mode 2.

The mode of operation must be established by writing a control word to the

PIO in the following format:

Listed in Table 1, Bits D7 and D6 form the binary code that designate mode

of operation:

Bits D5 and D4 are ignored. Bits D3-D0 must be set to 1111 to indicate

Set Mode.

Selecting Mode 0 enables any data written to the port output register by

the CPU to be enabled onto the port data bus. The output register contents

may be changed by writing a new data word to the port. Also, the current

contents of the output register may be read back to the Z80 CPU by

executing an input instruction.

When Mode 0 is active, a data write from the CPU causes the port’s

Ready handshake line to go High, thereby notifying the peripheral that

Table 1. PIO Mode Selection

D7 D6 Mode

0 0 0 (output)

0 1 1 (input)

1 0 2 (bidirectional)

113(control)

Mode Word

M1 M0 X X

Signifies Mode Word to be Set

D7 D6 D5 D4 D3 D0D2 D1

11 11

1 2 ... 204 205 206 207 208 209 210 211 212 213 214 ... 329 330

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Zilog Z08470 Manual de usuario Pagina 209