IRCC2.0 datasheet(80/87 Pages) SMSC

80 / 87 page

IOCHRDY Timer

The 10Fs IOCHRDY Timer is initialized when

IOCHRDY is active. The timer count sequence

is activated when IOCHRDY goes inactive.

IOCHRDY becomes active before the 10Fs time-

out has elapsed, the timer is stopped and the

count is re-initialized. If IOCHRDY is still inactive

when the 10Fs time-out occurs, the timer stops,

the time-out error bit is set, IOCHRDY is re-

asserted, and the string move bit is reset (Figure

49).

Zero Wait State Support

nSRDY

nSRDY can be driven by the IrCC 2.0 to indicate

that an access cycle shorter than the standard

I/O cycle can be executed.

Note: The names

nSRDY & nNOWS can be used interchangeably.

nSRDY is enabled by the No Wait bit in SCE

Configuration Register B. When No Wait is one,

nSRDY goes active following the trailing edge of

the ISA I/O command and inactive following the

rising edge (Figure 50). nSRDY is suppressed

during DMA & refresh cycles, i.e. when AEN is

active, or when IOCHRDY is inactive. Zero Wait

State support is only available when the SCE is

enabled.

String Move

IOCHRDY

IOR

FIFO Not Empty

AEN

24ns (max)

10us (max)

FIGURE 48 - VALID I/O READ READY CYCLE

String Move

IOCHRDY

IOR

FIFO Not Empty

AEN

10us

IOCHRDY Time-out

Start

Timer

IOCHRDY

Error

FIGURE 49 - IOCHRDY 10FS TIME-OUT

IRCC2.0 Datasheet(PDF) 80 Page - SMSC Corporation

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