In many cases, a simple blocking delay using delay.h is just fine, though. Using this peripheral will also allow non-blocking waits, and you will also be able to keep a 'system time' of some type. MPLAB ® XC8 User’s Guide for Embedded Engineers. Since it has its own clock and does not depend on what your cpu clock happens to be, you can switch cpu speeds as needed/wanted (and at runtime) and it will get you delays that are always correct. One alternative to using delay.h is to use the rtc peripheral which can have a fixed clock of 32kz (internal, or external if you have a 32k crystal).
#DELAY IN MPLAB XC8 SOFTWARE#
Display EEPROM Data Values on LEDsARun Code in MPLAB X IDEBGet Software and Hardware. Simply changing F_CPU to 3333333ul, will get you accurate delays for now (assuming fuse is OSC20M). View MPLAB CX16 GUIA DE USUARIO - DELAY.pdf from ELECTONICA 130 at. If you use delay.h, then you will have to set F_CPU to a value that matches what the cpu clock will be. 0 Transmit not in progress OR-ing this bit with SEN, RSEN, PEN, RCEN or ACKEN will indicate if the MSSP is in Idle mode. If you do not define F_CPU, then your delay will be ~3 times faster (delay thinks you are at 1MHz, but your cpu is at 3.33MHz). In I2C Master mode 1 transmit in progress (not including Ack and Stop bits), SSP1BUF is full. So when you inform delay.h your cpu is running at 20MHz, but is actually 6 times slower, your delay will be 6 times slower. If you want something other than DIV6, then you have to set the PDIV and PEN as needed (a CCP protected register). Out of reset, the clock CLKCTRL.MCLKCTRLB prescaler is ALWAYS enabled and set to DIV6, which means you get 3.33MHz or 2.66MHz depending on the FREQSEL fuse bits.
#DELAY IN MPLAB XC8 HOW TO#
This project demonstrates how to use it with MCC macros to control an output and. Its up to you to make sure F_CPU matches the actual clock speed.Ī 4809 (or any avr0/1) has two options for the cpu clock out of reset, set by the OSCCFG.FREQSEL fuse bits to either OSC20M or OSC16M. The MPLAB XC8 Compiler has a built-in delay function that can be handy. Here is my code, but it does not accept the.
#DELAY IN MPLAB XC8 MANUAL#
If you do not define F_CPU, then delay.h will still produce code but will assume 1MHz and warn you that F_CPU is not defined. The compiler user manual says that there is a delay function delayms(). Since delay.h creates code at compile time and has no idea what your clock is set to, you have to inform it via the F_CPU define. What's going on? A documentation error or something that I should learn / understand?į_CPU is used by delay.h to compute delay periods and has no effect on your actual cpu speed.
![delay in mplab xc8 delay in mplab xc8](https://sanuki-tech.net/pic/images/mplab-xc8-install-10.png)
but if I replace F_CPU with _XTAL_FREQ (which does not even appear in the compiler guide), the delay appears to work correctly! Document "MPLAB® XC8 C Compiler User’s Guide for AVR® MCU" (DS50002750C), page 133, section 7.5.1 states: "The macro F_CPU should be defined as aĬonstant that specifies the CPU clock frequency (in Hertz)." (It also mentions that optimizations need to be enabled for "accurate delay times".
![delay in mplab xc8 delay in mplab xc8](https://3.bp.blogspot.com/-57LHULfesqw/VCZO_vKsVfI/AAAAAAAAB0o/nW1De8dxQ0o/w1200-h630-p-k-no-nu/delays%2BC18.png)
In addition to very low delays, the compiler also messages: #warning "This file has been moved to. Issue: _delay_ms() macro runs about 5 times slower than it should.