EXTERNAL BUS
14-32
14.2.8.1
HOLD/HOLDA Protocol
In most cases, the i960 Jx processor controls the bus; an I/O peripheral (e.g., a communications
controller) requests bus control. The processor and I/O peripheral device exchange bus control
with two signals, HOLD and HOLDA.
HOLD is an i960 Jx processor synchronous input signal which indicates that the alternate master
needs the bus. HOLD may be asserted at any time so long as the transition meets the processors
setup and hold requirements. HOLDA (hold acknowledge) is the processor’s output which
indicates surrender of the bus. When the i960 Jx processor asserts HOLDA, it enters the Th (hold)
state (see
Figure 14.1
). If the last bus state was Ti or the last Tr of a bus transaction, the processor
is guaranteed to assert HOLDA and float the bus on the same clock edge in which it recognizes
HOLD. Similarly, the processor deasserts HOLDA on the same edge in which it recognizes the
deassertion of HOLD. Thus, bus latency is no longer than it takes the processor to finish any bus
access in progress.
If the bus is in hold and the 80960Jx needs to regain the bus to perform a transaction, the processor
does not deassert HOLDA. In many cases, however, it will assert the BSTAT pin (see section
14.2.8.2, BSTAT Signal
).
Unaligned load and store bus requests are broken into multiple accesses and the processor can
relinquish the bus between those transactions. When the alternate bus master gives control of the bus
back to the 80960Jx, the processor will immediately enter a Ta state to continue those accesses and
respond to any other bus requests. If no requests are pending, the processor will enter the idle state.
Figure 14-18
illustrates a HOLD/HOLDA arbitration sequence.
Содержание i960 Jx
Страница 1: ...Release Date December 1997 Order Number 272483 002 i960 Jx Microprocessor Developer s Manual ...
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Страница 25: ...1 INTRODUCTION ...
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Страница 35: ...2 DATA TYPES AND MEMORY ADDRESSING MODES ...
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Страница 47: ...3 PROGRAMMING ENVIRONMENT ...
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Страница 73: ...4 CACHE AND ON CHIP DATA RAM ...
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Страница 85: ...5 INSTRUCTION SET OVERVIEW ...
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Страница 111: ...6 INSTRUCTION SET REFERENCE ...
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Страница 195: ...INSTRUCTION SET REFERENCE 6 83 6 Opcode mov 5CCH REG movl 5DCH REG movt 5ECH REG movq 5FCH REG See Also LOAD STORE lda ...
Страница 233: ...7 PROCEDURE CALLS ...
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Страница 257: ...8 FAULTS ...
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Страница 291: ...9 TRACING AND DEBUGGING ...
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Страница 309: ...10 TIMERS ...
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Страница 325: ...11 INTERRUPTS ...
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Страница 369: ...12 INITIALIZATION AND SYSTEM REQUIREMENTS ...
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Страница 413: ...13 MEMORY CONFIGURATION ...
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Страница 429: ...14 EXTERNAL BUS ...
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Страница 469: ...15 TEST FEATURES ...
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Страница 493: ...A CONSIDERATIONS FOR WRITING PORTABLE CODE ...
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Страница 503: ...B OPCODES AND EXECUTION TIMES ...
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Страница 515: ...C MACHINE LEVEL INSTRUCTION FORMATS ...
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Страница 523: ...D REGISTER AND DATA STRUCTURES ...
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Страница 551: ...GLOSSARY ...
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Страница 561: ...INDEX ...
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