CHAPTER 9

PROGRAMMABLE COUNTER ARRAY

This chapter describes the programmable counter array (PCA), an on-chip peripheral of the 8XC251Sx that performs a variety of timing and counting operations, including pulse width mod- ulation (PWM). The PCA provides the capability for a software watchdog timer (WDT).

9.1PCA DESCRIPTION

The programmable counter array (PCA) consists of a 16-bit timer/counter and five 16-bit com- pare/capture modules. The timer/counter serves as a common time base and event counter for the compare/capture modules, distributing the current count to the modules by means of a 16-bit bus. A special function register (SFR) pair, CH/CL, maintains the count in the timer/counter, while five SFR pairs, CCAPxH/CCAPxL, store values for the modules (see Figure 9-1). Additional SFRs provide control and mode select functions as follows:

•The PCA timer/counter mode register (CMOD) and the PCA timer/counter control register (CCON) control the operation of the timer/counter. See Figure 9-7 on page 9-13 and Figure 9-8 on page 9-14.

•Five PCA module mode registers (CCAPMx) specify the operating modes of the compare/capture modules. See Figure 9-9.

For a list of SFRs associated with the PCA, see Table 9-1. For an address map of all SFRs, see Table 3-5 on page 3-17. Port 1 provides external I/O for the PCA on a shared basis with other functions. Table 9-2 identifies the port pins associated with the timer/counter and compare/cap- ture modules. When not used for PCA I/O, these pins can be used for standard I/O functions.

The operating modes of the five compare/capture modules determine the functions performed by the PCA. Each module can be independently programmed to provide input capture, output com- pare, or pulse width modulation. Module 4 only also has a watchdog-timer mode.

The PCA timer/counter and the five compare/capture modules share a single interrupt vector. The EC bit in the IE special function register is a global interrupt enable for the PCA. Capture events, compare events in some modes, and PCA timer/counter overflow all set flags in the CCON reg- ister. Setting the overflow flag (CF) generates a PCA interrupt request if the PCA timer/counter interrupt enable bit (ECF) in the CMOD register is set (Figure 9-1). Setting a compare/capture flag (CCFx) generates a PCA interrupt request if the ECCFx interrupt enable bit in the corre- sponding CCAPMx register is set (Figures 9-2 and 9-3). For a description of the 8XC251Sx in- terrupt system see Chapter 6, “Interrupt System.”

9-1

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Intel 8XC251SA, 8XC251SP, 8XC251SQ, 8XC251SB, Embedded Microcontroller Chapter Programmable Counter Array, PCA Description
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Embedded Microcontroller, 8XC251SP, 8XC251SA, 8XC251SQ, 8XC251SB 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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