87C251SP16 데이터 시트보기 (PDF) - Intel

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87C251SP16

HIGH-PERFORMANCE CHMOS MICROCONTROLLER

Intel 

8XC251SA/SB/SP/SQ HIGH-PERFORMANCE CHMOS MICROCONTROLLER

Table 6. Signal Descriptions (Continued)

Signal

Name

Type

Description

Alternate

Function

VPP

I Programming Supply Voltage. The programming supply voltage is EA#

applied to this pin for programming the on-chip OTPROM/EPROM.

VSS

VSS1

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, VSS1 can be unconnected

without loss of compatibility. (Not available on DIP)

VSS2

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, VSS2 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

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