80C251SB16 Datasheet, PDF (12/36 Pages) Intel Corporation – HIGH-PERFORMANCE CHMOS MICROCONTROLLER

8XC251SA/SB/SP/SQ HIGH-PERFORMANCE CHMOS MICROCONTROLLER
Table 6. Signal Descriptions (Continued)
Signal
Name
Type
Description
Alternate
Function
V_PP
I Programming Supply Voltage. The programming supply voltage is EA#
applied to this pin for programming the on-chip OTPROM/EPROM.
V_SS
V_SS1
GND Circuit Ground. Connect this pin to ground.
—
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_SS1 can be unconnected
without loss of compatibility. (Not available on DIP)
V_SS2
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_SS2 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 P1.6/CEX3
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.
WCLK
O Wait Clock Output. The real-time WCLK output is driven at port 1.7 P1.7/CEX4/
(WCLK) by writing a logical ‘1’ to the WCON.1 (RTWCE) bit at S:A7H. A17
When enabled, the WCLK output produces a square wave signal with
a period of one-half the oscillator frequency.
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.
† _{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).
12
PRELIMINARY