8xC251Tx Hardware Description

Table 2. 8xC251Tx Signal Descriptions (Sheet 1 of 3)

Signal

Type

Description

Alternate

Name

Function

 

 

 

 

 

 

A17

O

Address Line 17. Output to memory as the 18th external address bit

P1.7/CEX4/

 

 

(A17) in extended bus applications, depending on the values of bits

WCLK

 

 

RD0 and RD1 in configuration byte UCONFIG0 (see Chapter 4,

 

 

 

"Device Configuration," of the 8xC251SA, 8xC251SB, 8xC251SP,

 

 

 

8xC251SQ Embedded Microcontroller User’s Manual (272795). See

 

 

 

also RD# and PSEN#.

 

 

 

 

 

A16

O

Address Line 16. See RD#.

P3.7/RD#

 

 

 

 

A15:8*

O

Address Lines. Upper address lines for the external bus.

P2.7:0

 

 

 

 

A7:0

I/O

Address/Data Lines. Multiplexed lower address lines and data lines

P0/7:0

 

 

for external bus.

 

 

 

 

 

ALE

O

Address Latch Enable. ALE signals the start of an external bus

 

 

 

cycle and indicates that valid address information is available on lines

 

 

 

A15:8 and A7:0. An external latch can use ALE to demultiplex the

 

 

 

address from the address/data bus.

 

 

 

 

 

CEX0

I/O

Programmable Counter Array (PCA) input/output pins. These are

P1.3/TXD1

CEX1

 

input signals for the PCA capture mode and output signals for the

P1.4

CEX2

 

PCA compare mode and PCA PWM mode.

P1.5

CEX3

 

 

P1.6/WAIT#

CEX4

 

 

P1.7/A17/

 

 

 

WCLK

 

 

 

 

EA#

I

External Access. Direct program accesses to on-chip or off-chip

 

 

 

code memory. For EA# = 0, all program memory accesses are off

 

 

 

chip. For EA# = 1, all program memory accesses are on-chip if the

 

 

 

address is within the range of the on-chip program memory; other-

 

 

 

wise the access is off-chip. The value of EA# is latched at reset. For

 

 

 

devices without on-chip program memory, EA# must be strapped to

 

 

 

ground.

 

 

 

 

 

ECI

I

PCA External Clock Input. External clock input to the 16 bit PCA

P1.2/RXD1

 

 

timer.

 

 

 

 

 

INT1:0#

I

External Interrupts 0 and 1. These inputs set IE1:0 in the TCON

P3.3:2

 

 

register. If bits IT1:0 in the TCON register are set, units IE1:0 are set

 

 

 

by the falling edge on the INT1#/INT0#. If bits IT1:0 are clear, bits

 

 

 

IE1:0 are set by a low level on INTO1:0#.

 

 

 

 

 

P0.7:0

I/O

Port 0. This is an 8 bit, open drain, bidirectional I/O port.

AD7:0

 

 

 

 

P1.0

I/O

Port 1. This is an 8 bit, bidirectional I/O port with internal pullups.

T2

P1.1

 

 

T2EX

P1.2

 

 

ECI/RXD1

P1.3

 

 

CEX0/TXD1

P1.4

 

 

CEX1

P1.5

 

 

CEX2

P1.6

 

 

CEX3/WAIT#

P1.7

 

 

CEX4/A17/

 

 

 

WCLK

 

 

 

 

P2.7:0

I/O

Port 2. This is an 8 bit, bidirectional I/O port with internal pullups.

A15:8

 

 

 

 

*The descriptions of A15:8/P2.7:0 and AD7:0/P0.7:0 are for non page mode configuration. If configured in page mode, Port 0 carries the lower address bits (A7:0) and Port 2 carries the upper address bits (A15:8) and the data (D7:0)

3

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Intel 8XC251SQ, 8xC251TB, 8XC251SA XC251Tx Signal Descriptions Sheet 1, Signal Type Description Alternate Name Function
Page 8 Page 10

8XC251SP, 8XC251SA, 8XC251SQ, 8xC251TB, 8xC251TQ specifications

The Intel 8XC251 series of embedded microcontrollers is a family of versatile and powerful devices, designed to meet the demands of a wide range of applications. With models such as the 8XC251SB, 8XC251SQ, 8XC251SA, and 8XC251SP, this series offers unique features while maintaining a high level of performance and reliability.

At the heart of the 8XC251 microcontrollers is the 8051 architecture, which provides a 16-bit processor capable of executing complex instructions efficiently. This architecture not only allows for a rich instruction set but also facilitates programming in assembly language and higher-level languages like C, which are essential for developing sophisticated embedded systems.

One of the significant features of the 8XC251 family is its integrated peripherals, including timer/counters, serial communication interfaces, and interrupt systems. These peripherals enable developers to implement timing functions, data communication, and real-time processing, all of which are crucial in modern embedded applications. The 8XC251SB and 8XC251SQ models, for instance, come equipped with multiple I/O ports that allow for interfacing with other devices and systems, enhancing their functionality in various environments.

The memory architecture of the 8XC251 devices is noteworthy, featuring on-chip ROM, RAM, and EEPROM. The on-chip memory allows for fast access times, which is essential for executing programs efficiently. Moreover, the EEPROM serves as non-volatile memory, enabling the storage of configuration settings and important data that must be retained even when power is lost.

In terms of operating voltage, the 8XC251 devices are designed to operate in a wide range, typically between 4.0V and 6.0V. This flexibility makes them suitable for battery-powered applications, where energy efficiency is critical. The power management features, including reduced power modes, further enhance their suitability for portable devices.

Lastly, the 8XC251 series is supported by a wide range of development tools and resources, allowing engineers and developers to streamline the development process. This support, combined with the microcontrollers' robust features, makes the Intel 8XC251 family a reliable choice for various embedded applications, such as industrial automation, automotive systems, and consumer electronics.

Overall, the Intel 8XC251SB, 8XC251SQ, 8XC251SA, and 8XC251SP deliver high performance, versatility, and ease of use, making them a preferred choice for embedded system designers looking to develop efficient and effective solutions.
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