TMP91C824
91C824-55
2008-02-20
Note about bus release and programmable pull-up I/O port pins
When the bus is released (e.g., when
BUSAK
=
0), the output buffers for D0 to D15, A0 to
A23, and the control signals (
RD
,
WR
,
HWR
,
W
/
R
and
0
CS
to
3
CS
, EA24, EA25,
CS2A
to
2E
) are off and are set to high impedance.
However, the output of built-in programmable pull-up resistors are kept before the bus is
released. These programmable pull-up resistors can be selected ON/OFF by programmable
when they are used as the input ports.
When they are used as output ports, they cannot be turned ON/OFF in software.
Table 3.5.4 shows the pin states after the bus has been released.
Table 3.5.4 Pin States (after bus release)
The Pin State (when the bus is released)
Pin Name
Port Mode
Function Mode
D0 to D7
Become high impedance (High-Z).
D8 to D15 (P10 to P17)
The state is not changed.
(Do not become to high impedance
(High-Z).)
A0 to A15
First sets all bits to high, then sets them to
high impedance (High-Z).
A16 to 23 (P20 to P27)
The state is not changed.
(Do not become to high impedance
(High-Z).)
RD
WR
PZ2 (
HWR
),
PZ3 (R/
W
),
The state is not changed.
(Do not become to high impedance
(High-Z).)
First sets all bits to high, then the output
buffer is OFF. The programmable pull-up
resistor is ON irrespective of the output
latch.
P60 (
CS0
), P61 (
CS1
),
P62 (
CS2
,
CS2A
),
P63 (
CS3
),
First sets all bits to high, then sets them to
high impedance (High-Z).