Файл: BASCOM AVR, help reference (2007).pdf

© MCS Electronics, 1995-2007

BASCOM HARDWARE

Additional Hardware

Of course just running a program on the chip is not enough. You will probably attach many types of electronic devices to the processor ports.

BASCOM supports a lot of hardware and so it has lots of hardware related statements. Before explaining about programming the additional hardware, it might be better to talk about the chip.

The AVR internal hardware

Attaching an LCD display

Using the I2C protocol

Using the 1WIRE protocol

Using the SPI protocol

You can attach additional hardware to the ports of the microprocessor. The following statements will then be able to be used:

I2CSEND and I2CRECEIVE and other I2C related statements.

CLS,LCD,DISPLAY and other related LCD-statements.

1WRESET , 1WWRITE and 1WREAD

AVR Internal Hardware

The AVR chips all have internal hardware that can be used.

For this description of the hardware the 90S8515 was used. Newer chips like the Mega8515 may differ and have more or less internal hardware.

You will need to read the manufacturers data sheet for the processor you are using to earnl about the special internal hardware available.

Timer / Counters

The AT90S8515 provides two general purpose Timer/Counters - one 8-bit T/C and one 16-bit T/C. The Timer/Counters have individual pre-scaling selection fromthe same 10-bit pre-scaling timer. Both Timer/Counters can either be used as a timer with an internal clock time base or as a counter with an external pin connection which triggers the counting.

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© MCS Electronics, 1995-2007

More about TIMERO

More about TIMER1

The WATCHDOG Timer

Almost all AVR chips have the ports B and D. The 40 or more pin devices also have ports A and C that also can be used for addressing an externalRAM chip (XRAM). Since all ports are similar except that PORT B and PORT D have alternative functions, only these ports are described.

PORT B

PORT D

AVR Internal Registers

You can manipulate the internal register values directly from Bascom. They are also reserved words. Each register acts like a memory location or programvariable, except that the bits of each byte have a special meaning. The bits control how the internal hardware functions, or report the status of internal hardware functions. Read the data sheet to determine what each bit function is for.

The internal registers for the AVR90S8515 are : (other processors are similar, but vary)

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The registers and their addresses are defined in the xxx.DAT files which are placed in the BASCOM-AVR application directory.

The registers can be used as normal byte variables.

PORTB = 40 will place a value of 40 into port B.

Note that internal registers are reserved words. This means that they can't be dimensioned as BASCOM variables!

So you can't use the statement DIM SREG As Byte because SREG is an internal register.

You can however manipulate the register with the SREG = value statement, or var = SREG statement.

AVR Internal Hardware TIMER0

The 8-Bit Timer/Counter0

The 90S8515 was used for this example. Other chips might have a somewhat different timer.

The 8-bit Timer/Counter0 can select its clock source from CK, pre-scaled CK, or an external pin. In addition it can be stopped (no clock).

The overflow status flag is found in the Timer/Counter Interrupt Flag Register - TIFR. Control signals are found in the Timer/Counter0 Control Register - TCCR0. The interrupt enable/disable settings for Timer/Counter0 are found in the Timer/Counter Interrupt Mask Register - TIMSK.

When Timer/Counter0 is externally clocked, the external signal is synchronized with the oscillator frequency of the CPU. To assure proper sampling of the external clock, the minimum time between two external clock transitions must be at least one internal CPU clock period. The external clock signal is sampled on the rising edge of the internalCPU clock.

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© MCS Electronics, 1995-2007

Interrupt Mask Register - TIMSK.

When Timer/Counter1 is externally clocked, the external signal is synchronized with the oscillator frequency of the CPU. To assure proper sampling of the external clock, the minimum time between two external clock transitions must be at least one internal CPU clock period.

The external clock signal is sampled on the rising edge of the internal CPU clock.

The 16-bit Timer/Counter1 features both a high resolution and a high accuracy usage with lower pre-scaling values.

Similarly, high pre-scaling values make the Timer/Counter1 useful for lower speed functions or exact timing functions with infrequent actions.

The Timer/Counter1 supports two Output Compare functions using the Output Compare Register 1 A and B -OCR1A and OCR1B as the data values to be compared to the Timer/Counter1 contents.

The Output Compare functions include optional clearing of the counter on compareA match, and can change the logic levels on the Output Compare pins on both compare matches.

Timer/Counter1 can also be used as a 8, 9 or 10-bit Pulse Width Modulator (PWM). In this mode the counter and the OCR1A/OCR1B registers serve as a dual glitch-free stand-alone PWM with centered pulses.

The Input Capture function of Timer/Counter1 provides a capture of the Timer/Counter1 value to the Input Capture Register - ICR1, triggered by an externalevent on the Input Capture Pin - ICP. The actual capture event settings are defined by the Timer/Counter1 Control Register -TCCR1B.

In addition, the Analog Comparator can be set to trigger the Capture.

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© MCS Electronics, 1995-2007

AVR Internal Hardware Watchdog timer

The Watchdog Timer

The Watchdog Timer is clocked from a separate on-chip oscillator which runs at approximately 1MHz. This is the typical value at VCC = 5V.

By controlling the Watchdog Timer pre-scaler, the Watchdog reset interval can be adjusted from 16K to 2,048K cycles (nominally 16 - 2048 ms). The Bascom RESET WATCHDOG - instruction resets the Watchdog Timer.

Eight different clock cycle periods can be selected to determine the reset period.

If the reset period expires without another Watchdog reset, the AT90Sxxxx resets and program execution starts at the reset vector address.

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