8XC151SA/SB HIGH-PERFORMANCE CHMOS MICROCONTROLLER
Table 7. Signal Descriptions
(Continued)
Signal
Name
Type
Description
Multiplexed
With
P3.0
P3.1
P3.3:2
P3.5:4
P3.6
P3.7
I/O
Port 3.
This is an 8-bit, bidirectional I/O port with internal pullups.
RXD
TXD
INT1:0
Y
T1:0
WR
Y
RD
Y
PSEN
Y
O
Program Store Enable.
Read signal output. This output is asserted
for a memory address range that depends on bits RD0 and RD1 in
configuration byte UCONFIG0.
D
RD
Y
O
Read.
Read signal output to external data memory.
P3.7
RST
I
Reset.
Reset input to the chip. Holding this pin high for 64 oscillator
periods while the oscillator is running resets the device. The port pins
are driven to their reset conditions when a voltage greater than V
IH1
is
applied, whether or not the oscillator is running. This pin has an
internal pulldown resistor, which allows the device to be reset by
connecting a capacitor between this pin and V
CC
.
Asserting RST when the chip is in idle mode or powerdown mode
returns the chip to normal operation.
D
RXD
I/O
Receive Serial Data.
RXD sends and receives data in serial I/O
mode 0 and receives data in serial I/O modes 1, 2, and 3.
P3.0
T1:0
I
Timer 1:0 External Clock Inputs.
When timer 1:0 operates as a
counter, a falling edge on the T1:0 pin increments the count.
P3.5:4
T2
I/O
Timer 2 Clock Input/Output.
For the timer 2 capture mode, this
signal is the external clock input. For the clock-out mode, it is the
timer 2 clock output.
P1.0
T2EX
I
Timer 2 External Input.
In timer 2 capture mode, a falling edge
initiates a capture of the timer 2 registers. In auto-reload mode, a
falling edge causes the timer 2 registers to be reloaded. In the up-
down counter mode, this signal determines the count direction:
1
e
up, 0
e
down.
P1.1
TXD
O
Transmit Serial Data.
TXD outputs the shift clock in serial I/O mode
0 and transmits serial data in serial I/O modes 1, 2, and 3.
P3.1
V
CC
PWR
Supply Voltage.
Connect this pin to the
a
5V supply voltage.
D
V
CC2
PWR
Secondary Supply Voltage 2.
This supply voltage connection is
provided to reduce power supply noise. Connection of this pin to the
a
5V supply voltage is recommended. However, when using the
8XC151SA/SB as a pin-for-pin replacement for the 8XC51FX, V
SS2
can be unconnected without loss of compatibility. (Not available on
DIP)
D
V
PP
I
Programming Supply Voltage.
The programming supply voltage is
applied to this pin for programming the on-chip OTPROM.
EA
Y
2
The descriptions of A15:8/P2.7:0 and AD7:0/P0.7:0 are for the nonpage-mode chip configuration (compatible with
44-lead PLCC and 40-pin DIP MCS 51 microcontrollers). If the chip is configured for page-mode operation, port 0 carries
the lower address bits (A7:0), and port 2 carries the upper address bits (A15:8) and the data (D7:0).
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