The accumulator, r0r7 registers and b register are 1byte value registers. Special function registers are upper ram memory in the 8051 microcontroller. Tmod stands for timer mode control register intel 8051 microcontroller register. Download pdf document for 805189c51,89c52 microcontroller timers registers. In this tmod register, lower 4 bits are set aside for. This register, which holds the address, is called the pointer register and is said to point to the operand. As 8051 has 8bit architecture, each timer register is treated as two 8bit registers namely th0, tl0, th1, tl1. It is a 16bit register and accessed as low byte and high byte. M1 m0 mode description 0 0 mode 0 bit timer 0 1 mode 1 16bit timer 1 0 mode 2 8bit auto reload 1 1 mode 3 split timer mode april 10 9. These registers can be accessed like any other register. How to use internal timer registers of 805189c51,89c52. The value of n, in above equation, is determined based of smod.
The sfr register is implemented by bitaddress registers and byteaddress. The data pointer dptr is the 8051s only useraccessible 16bit 2byte register. Only registers r0, r1 and dptr can be used as pointer registers. There are 21 special function registers sfr in 8051 micro controller and this includes register a, register b, processor status word psw, pcon etc etc. When used as counters, the microcontroller counts the external clock pulses provided on pin 3. Gate bit was used to enable and disable the timer 1 by means of a signal brought into the interrupt pin. Counters and timers in 8051 microcontroller contain two special function registers. Know about types of registers in 8051 microcontroller. Apr 05, 2018 8051 timers register description tmod register. Timers and counters in 8051 microcontroller baud rate. Tmod is nothing but a 8 bit register used for configuring the timer for desired operation. Timercounter mode control tmod register, bits 2 and 6 respectively. Jun 26, 2018 8051 has two 16bit timers, which can also be used as counters by setting the appropriate bits in the tmod registers. This bit in tmod register is used to know whether it is used as a delay generator or as an event counter.
Lower 4bits are used for control operation of timer 0. It is used by the 8051 to access external memory using the address indicated by dptr. Aug 08, 2019 tmod timer mode register of 8051 microcontroller tmod is an eight bit register, it is bit addressable. Multiple choice questions and answers on microcontrollers and. Atmel 8051 microcontrollers hardware 1 0509c80510706 section 1 8051 microcontroller instruction set for interrupt response time information, refer to the hardware description chapter.
There are 21 unique locations for these 21 special function registers and each of these register is of 1 byte size. Tmod timer mode register tcon timer control register thx timer high register x means weather 0 or 1. In this tmod register, lower 4 bits are set aside for timer0 and the upper 4 bits are set aside for timer1. The 251 provides two additional status flags, z and n, that are available in a second special function register called psw1.
This timer is used to set various timer modes in timer0. Timer1 is also a 16bits register, which is split into two bytes, referred to as tl1 and th1. When the 8051 is first booted up, register bank 0 addresses 00h through 07h is used by default. Multiprocessor communication with 8051 microcontroller. In the case of timers, register is incremented once every machine cycle. Both can be configured to operate either as timers or as event counters. This bit in the tmod register is used to decide whether a timer is used as a delay generator or an event. The format of tmod register is, the lower four bits of tmod register is used to control timer 0 and the upper four bits are used to control timer1. Mov r0, a the instruction transfers the accumulator content into the r0 register. Dec 08, 2016 54 which bit must be set in tcon register in order to start the timer 0 while operating in mode 0. The registers tcon and tmod affect the timer operation. This register contain not only the mode selection bits but also the 9th data bit for transmit and receive tb8 and rb8 and the serial part interrupt bits ti and ri. The two timers can be independently program to operate in various modes.
In mode1 the th and tl registers are cascaded to form 16bit timer register. These two timers and counters in 8051 microcontroller have four operating modes, which are selected by bitpairs ml, m0 in tmod. Internal operation of the 8051 timer same for both timers timer registers tcon timer control tmod timer mode th0tl0 timer 0 16 bit register byte addressable only th1tl1 timer 1 16 bit register byte addressable only tcon tcon sfr and its individual bits it0it1. Dec 07, 2016 8051 theory tmod register electrogram. Tcon and tmod timer registers of 8051 microcontroller. The lower four bits of tmod register is used to control timer0 and the upper four bits are used to control timer. Register addressing the register addressing instruction involves information transfer between registers example. Uart, rs232 in this tutorial, we are going to discuss the serialuart communication of 8051. To interface these devices to the outside world, input and output devices, like keypad and lcds respectively, are generally used 2.
Mode 0bit counter 8192 input pulses mode 116bit counter 65536 input pulses mode 28 bit. Interfacing dac and adc with 8051 microcontroller 8051 assembly language programming. Interfacing dac and adc with 8051 microcontroller 8051 assembly language programming duration. Serial port control register scon of 80518031 microcontroller the format of scon register is shown. To select the operating mode and the timercounter operation of the timers we use tmod register.
Cpu registers provide explanations to the following register types. The timer or counter mode is selected by control bits ct in the special function register tmod. Timercounter special function registerstmod m0 and m1 bits are used to set timer mode the same for timer0 and timer1 8051 delivers 4 timer modes. The lowbyte register is called tl0 timer 0 low byte and the highbyte register is called th0 timer 0 high byte. Creating time delay using timers in 8051 microcontroller. Both of these registers use the same register called tmod to set various timer operation modes. Timercounter special function registerstmod lower 4 bits are for timer0. For the love of physics walter lewin may 16, 2011 duration. In the indirect addressing mode, a register is used to hold the effective address of the operand. In addition to the cpu registers r0 r7, all x51 variants have an sfr space that is used to address onchip peripherals and io ports. The register bank bank 0, 1, 2 or 3 must be specified prior to this instruction. It is an 8 bit register used solely for serial communication in the 8051. Nov 02, 2011 this bit in tmod register is used to know whether it is used as a delay generator or as an event counter. Scon register also consists of bits that are automatically set when a byte of data is transmitted or received.
Since the 8051 follows an 8bit architecture, each 16 bit is accessed as two separate registers of lowbyte and highbyte. In fact, by manipulating the 8051 microcontroller special function registers sfrs, you can assess or change the operating mode of the 8051 microcontroller. Timer 0 and timer 1 are two timer registers in 8051. The 16bit register of timer 0 is accessed as low and highbyte. The 8051 variants provide one special function register called psw with this status information. When used as timers, the 8051 timers count up every 12th clock cycle. Serial port control and status register is the special function register scon. After understating the basics of 8051 uart module, we will see how to use the exploreembedded libraries to communicate with any of the uart devices.
These registers contain all peripheral related registers like p0, p1, p2, p3, timers or counters, serial port and interruptsrelated registers. The serial port of 8051 microcontroller supports full duplex communication i. The low byte is referred as tl0 and the high byte is referred as th0. Before programming we should know the timer registers.
Operations on sfr byte address 208 or bit addresses 209215 that is, the psw or bits in the psw also affect flag setti ngs. Dec 08, 2012 timercounter special function registers tmod m0 and m1 bits are used to set timer mode the same for timer0 and timer1 8051 delivers 4 timer modes. The 8051 timer and counter are the same units, but in this tutorial, we will discuss only the timer unit to simplify the discussion. Tmod timer mode register and tcon timer control register, which are used for activating and configuring timers and counters. These timers and counters in 8051 microcontroller are present in both the 8051 and the 8052. Serial mode bit is used to determine the serial communication port baud rate with timer 1. A byte of data to be transferred via the txd line must be placed in. Find the value for tmod if we want to program timer 0 in mode 2, use 8051 xtal for the clock source. Tmod is listed in the worlds largest and most authoritative dictionary database of abbreviations and acronyms. Timer1 registers is also a 16 bits register and is split into two bytes, referred to as tl1 and th1. This is an 8bit register which is used by both timers 0 and 1 to set the various timer modes. Tmod and tcon registers are used for setting and using these timerscounters. Tmodtimer mode register of 8051 microcontroller tmod is an eight bit register, it is bit addressable.
The clock source for the time delay is the crystal frequency of 8051. Registers in 8051 math register indicates that each bit a of the register can be programmed. If this pin is high, then corresponding timer is enabled when there is an interrupt at corresponding int pin of the microcontroller. A byte of data to be transferred via the txd line must be placed in the sbuf register.
Sep 06, 2018 for the love of physics walter lewin may 16, 2011 duration. Timer mode control register tmod of 80518031 microcontroller. The tmod register has two separate two bit field m0 and ml to program the operating. Higher four bits 4 to 7 are related to timer 1 where as the lower four bits 0 to 3 perform the exact same functions, but for timer 0. The tl register will function as 8bit timer count register and the th register will hold an initial count value. Find the timers clock frequency and its period for various 8051based systems with the following crystal frequencies. Microcontroller timers counters tmod tcon microcontroller.
Tmod is an 8bit register used for selecting timer or counter and mode of timers. The program status word psw contains status bits that reflect the current cpu state. Ct 0, then it is used as a timer for time delay generation. Find the value for tmod if we want to program timer 0. It indicates timer 0 or timer 2 tlx timer low register x means weather 0 or 1. Tmod is defined as timer mode control register intel 8051 microcontroller register rarely. Special function registers ip, ie, tmod, tcon, scon, and pcon contain control and status bits for the interrupt system, the timercounters, and the serial port. Timers in 8051 microcontroller and their programming. Mode2 o in mode2, the timers function as 8bit timer with automatic reload feature. In this paper the serial rs485 mode of communication using 8051 is the main concern, with an emphasis on interfacing it with lcd hitachi 44780. Nov 30, 2017 the 8051 microcontroller special function registers are used to program and control different hardware peripherals like timers, serial port, io ports etc. Operating mode selection register and tcon timercounter operation control register, higher and lower order bytes of individual timercounters.
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