Preliminary – Intel 8XC251SA User Manual
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PRELIMINARY
8XC251SA/SB/SP/SQ HIGH-PERFORMANCE CHMOS MICROCONTROLLER
V
PP
I
Programming Supply Voltage. The programming supply voltage is
applied to this pin for programming the on-chip OTPROM/EPROM.
EA#
V
SS
GND
Circuit Ground. Connect this pin to ground.
—
V
SS
1
GND
Secondary Ground. This ground is provided to reduce ground bounce
and improve power supply bypassing. Connection of this pin to ground
is recommended. However, when using the 8XC251SA/SB/SP/SQ as
a pin-for-pin replacement for the 8XC51BH, V
SS
1
can be unconnected
without loss of compatibility. (Not available on DIP)
—
V
SS
2
GND
Secondary Ground 2. This ground is provided to reduce ground
bounce and improve power supply bypassing. Connection of this pin to
ground is recommended. However, when using the 8XC251SB as a
pin-for-pin replacement for the 8XC51FX, V
SS
2
can be unconnected
without loss of compatibility. (Not available on DIP)
—
WAIT#
I
Real-time Wait State Input. The real-time WAIT# input is enabled by
writing a logical ‘1’ to the WCON.0 (RTWE) bit at S:A7H. During bus
cycles, the external memory system can signal ‘system ready’ to the
microcontroller in real time by controlling the WAIT# input signal on the
port 1.6 input.
P1.6/CEX3
WCLK
O
Wait Clock Output. The real-time WCLK output is driven at port 1.7
(WCLK) by writing a logical ‘1’ to the WCON.1 (RTWCE) bit at S:A7H.
When enabled, the WCLK output produces a square wave signal with
a period of one-half the oscillator frequency.
P1.7/CEX4/
A17
WR#
O
Write. Write signal output to external memory.
P3.6
XTAL1
I
Input to the On-chip, Inverting, Oscillator Amplifier. To use the
internal oscillator, a crystal/resonator circuit is connected to this pin. If
an external oscillator is used, its output is connected to this pin. XTAL1
is the clock source for internal timing.
—
XTAL2
O
Output of the On-chip, Inverting, Oscillator Amplifier. To use the
internal oscillator, a crystal/resonator circuit is connected to this pin. If
an external oscillator is used, leave XTAL2 unconnected.
—
Table 6. Signal Descriptions (Continued)
Signal
Name
Type
Description
Alternate
Function
†
The descriptions of A15:8/P2.7:0 and AD7:0/P0.7:0 are for the nonpage-mode chip configuration (com-
patible with 44-pin 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).