Zilog Z08470 Manual do Utilizador descarregar pdf (Página 300)

UM008101-0601 Serial Input/Output

280

data. The Wait function is selected by setting D6 to 0. If this bit is 0, the

WAIT/READY output is in the open-drain state and goes Low when active.

Both the Wait and Ready functions can be used in either the Transmit or

Receive modes, but not both simultaneously. If D5 (Wait/Ready on Receive/

Transmit) is set to 1, the Wait/Ready function responds to the condition of

the receive buffer (empty or full). If D5 is set to 0, the Wait/Ready function

responds to the condition of the transmit buffer (empty or full).

The logic states of the WAIT

/READY output, which are either active or

inactive, depend on the combination of modes selected. Table 18 summa-

rizes these combinations.

The WAIT

output High-to-Low transition occurs at the delay time

tDIC(WR) after the I/O request. The Low-to-High transition occurs at the

delay tDHΦ(WR) at the falling edge of Φ. The READY output High-to-

Low transition occurs at the delay tDLΦ(WR) at the rising edge of Φ.The

READY output Low-to-High transition occurs at the delay tDIC(WR)

after IORQ

falls.

The Ready function can occur when the Z80 SIO is not selected. When

the READY

output becomes active Low, the DMA controller issues

Table 18. Wait/Ready Functions

If D7 = 0

and D6 = 1 and D6 = 0

READY is High WAIT is floating

If D7 = 0

and D5 = 0 and D5 = 1

READY is High when transmit buffer is full READY is High when receive buffer is empty

WAIT is low when transmit buffer is full and

S10dataportisanselected

WAIT is Low when receive buffer is empty

and SID data port is selected

READY is Low when transmit buffer is empty READY is Low when receive buffer is full

WAIT is floating when transmit buffer is empty WAIT is floating when receive buffer is full

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