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3-19
BUS INTERFACE UNIT
Figure 3-18. Normally Ready System Timings
Conditions causing the BIU to become idle include the following.
• The instruction prefetch queue is full.
• An effective address calculation is in progress.
• The bus cycle inherently requires idle states (e.g., interrupt acknowledge, locked opera-
tions).
• Instruction execution forces idle states (e.g., HLT, WAIT).
ARDY
CLKOUT
In a Normally-Ready system, a wait state will be inserted when 1 & 2 are met.
(Assumes SRDY is low.)
T2 T3 TW
ARDY
CLKOUT
Alternatively, in a Normally-Ready system, a wait state will be inserted
when1 & 2 are met for SRDY and ARDY.
1. T
ARYCL
, T
SRYCL
: ARDY and SRDY low to clock low
2. T
CHARX
, T
CLSRY
: ARDY and SRDY low from clock low
T2 T3 TW
1
2
1
2
!
Failure to meet ARDY and SRDY setup and hold can cause a device failure
(i.e., the bus hangs or operates inappropriately).
1. T
ARYCH
: ARDY low to clock high
2. T
ARYCHL
: Clock high to ARDY high (ARDY inactive hold time)
SRDY
T4
T4
A1512-0A