376 datasheet(54/95 Pages) INTEL

54 / 95 page

376 EMBEDDED PROCESSOR

240182 – 31

NOTE

For maximum design flexibility the 80376 has no internal pull-up resistors on its outputs Your design may require an

external pullup on ADS and other 80376 outputs to keep them negated during float periods

Figure 416 Requesting Hold from Idle Bus

RESET DURING HOLD ACKNOWLEDGE

RESET being asserted takes priority over HOLD be-

ing asserted If RESET is asserted while HOLD re-

mains asserted the 80376 drives its pins to defined

states during reset as in Table 45 Pin State Dur-

ing Reset

and performs internal reset activity as

usual

If HOLD remains asserted when RESET is inactive

the 80376 enters the hold acknowledge state before

performing its first bus cycle provided HOLD is still

asserted when the 80376 processor would other-

wise perform its first bus cycle If HOLD remains as-

serted when RESET is inactive the BUSY input is

still sampled as usual to determine whether a self

test is being requested

FLOAT

Activating the FLT input floats all 80376 bidirectional

and output signals including HLDA Asserting FLT

isolates the 80376 from the surrounding circuitry

When an 80376 in a PQFP surface-mount package

is used without a socket it cannot be removed from

the printed circuit board The FLT input allows the

80376 to be electrically isolated to allow testing of

external circuitry This technique is known as ONCE

for ‘‘ON-Circuit Emulation’’

ENTERING AND EXITING FLOAT

FLT is an asynchronous active-low input It is recog-

nized on the rising edge of CLK2 When recognized

it aborts the current bus cycle and floats the outputs

of the 80376 (Figure 420) FLT must be held low for

a minimum of 16 CLK2 cycles Reset should be as-

serted and held asserted until after FLT is deassert-

ed This will ensure that the 80376 will exit float in a

valid state

Asserting the FLT input unconditionally aborts the

current bus cycle and forces the 80376 into the

FLOAT mode Since activating FLT unconditionally

forces the 80376 into FLOAT mode the 80376 is not

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