Enhanced Am486 Microprocessor
AMD
37
PRELIMINARY
5.4
Table 9 shows the pin states during Stop Grant Bus
states. During the Stop Grant state, most output and
input/output signals of the microprocessor maintain the
level they held when entering the Stop Grant state. The
data and data parity signals are three-stated. In response to
HOLD being driven active during the Stop Grant state (when
the CLK input is running), the CPU generates HLDA and
three-states all output and input/output signals that are three-
stated during the HOLD/HLDA state. After HOLD is deassert-
ed, all signals return to the same state they were before the
HOLD/HLDA sequence.
Pin State during Stop Grant
Table 9. Pin State During Stop Grant Bus State
Signal
Type
State
A3–A2
O
Previous State
A31–A4
I/O
Previous State
D31–D0
I/O
Floated
BE3–BE0
O
Previous State
DP3–DP0
I/O
Floated
W/R, D/C, M/IO, CACHE
O
Previous State
ADS
O
Inactive
LOCK, PLOCK
O
Inactive
BREQ
O
Previous State
HLDA
O
As per HOLD
BLAST
O
Previous State
FERR
O
Previous State
PCHK
O
Previous State
SMIACT
O
Previous State
HITM
O
Previous State
To achieve the lowest possible power consumption dur-
ing the Stop Grant state, the system designer must en-
sure the input signals with pull-up resistors are not
driven Low, and the input signals with pull-down resis-
tors are not driven High.
All inputs except data bus pins must be driven to the
power supply rails to ensure the lowest possible current
consumption during Stop Grant or Stop Clock modes.
For compatibility, data pins must be driven Low to
achieve the lowest possible power consumption.
5.5
Figure 20 shows the state transitions during a Stop
Clock cycle.
Clock Control State Diagram
5.5.1
This is the normal operating state of the CPU. While in
the normal state, the CLK input can be dynamically
changed within the specified CLK period stability limits.
Normal State
5.5.2
The Stop Grant state provides a low-power state that
can be entered by simply asserting the external STPCLK
interrupt pin. When the Stop Grant bus cycle has been placed
on the bus, and either RDY or BRDY is returned, the CPU is
in this state. The CPU returns to the normal execution state
10–20 clock periods after STPCLK has been deasserted.
Stop Grant State
While in the Stop Grant state, the pull-up resistors on
STPCLK and UP are disabled internally. The system must
continue to drive these inputs to the state they were in imme-
diately before the CPU entered the Stop Grant State. For min-
imum CPU power consumption, all other input pins should be
driven to their inactive level while the CPU is in the Stop Grant
state.
.
t
20
t
21
Figure 19. Entering Stop Grant State
RDY
ADDR
STPCLK
CLK
Stop Grant Bus cycle