TIMER/COUNTERS AND WATCHDOG TIMER

8.4.1Mode 0 (13-bit Timer)

Mode 0 configures timer 0 as a 13-bit timer, which is set up as an 8-bit timer (TH1 register) with a modulo-32 prescalar implemented with the lower 5 bits of the TL1 register (Figure 8-2). The upper 3 bits of the TL1 register are ignored. Prescalar overflow increments the TH1 register.

8.4.2Mode 1 (16-bit Timer)

Mode 1 configures timer 1 as a 16-bit timer with TH1 and TL1 connected in cascade (Figure 8-2). The selected input increments TL1.

8.4.3Mode 2 (8-bit Timer with Auto-reload)

Mode 2 configures timer 1 as an 8-bit timer (TL1 register) with automatic reload from the TH1 register on overflow (Figure 8-3). Overflow from TL1 sets overflow flag TF1 in the TCON reg- ister and reloads TL1 with the contents of TH1, which is preset by software. The reload leaves TH1 unchanged. See section 8.5.1, “Auto-load Setup Example.”

8.4.4Mode 3 (Halt)

Placing timer 1 in mode 3 causes it to halt and hold its count. This can be used to halt timer 1 when the TR1 run control bit is not available, i.e., when timer 0 is in mode 3. See the final para- graph of section 8.4, “Timer 1.”

8.5TIMER 0/1 APPLICATIONS

Timer 0 and timer 1 are general purpose timers that can be used in a variety of ways. The timer applications presented in this section are intended to demonstrate timer setup, and do not repre- sent the only arrangement nor necessarily the best arrangement for a given task. These examples employ timer 0, but timer 1 can be set up in the same manner using the appropriate registers.

8.5.1Auto-load Setup Example

Timer 0 can be configured as an eight-bit timer (TL0) with automatic reload as follows:

1.Program the four low-order bits of the TMOD register (Figure 8-5) to specify: mode 2 for

timer 0, C/T0# = 0 to select FOSC/12 as the timer input, and GATE0 = 0 to select TR0 as the timer run control.

2.Enter an eight-bit initial value (n0) in timer register TL0, so that the timer overflows after the desired number of peripheral cycles.

8-9

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Intel 8XC251SB, 8XC251SA, 8XC251SP, 8XC251SQ manual Mode 3 Halt, Timer 0/1 Applications, Auto-load Setup Example
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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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