DATA TRANSFER SCHEMES OF 8085
- 1. 8051 Microcontroller Data Transfer Schemes PREPAREDBY B.SARAVANAMANIKANDAN ASSISTANTPROFESSOR Kongunaducollegeof engineeringandtechnology
- 2. SERIAL INTERFACE • Data transfer between memory and register, register and port and port to outside unit in these data transfers, a byte is transferred between two units. • Thus 8 bits are transferred in parallel. • This type of data transfer is mostly used for short distance, data transfer. • When data becomes more than few meters the parallel data transfer suffers from phenomenon called bit skewing. KNCET EEE DEPARTMENT
- 3. ASYCHRONOUS and SYNCHRONOUS • In synchronous communication the transmission from one device and receipt at other devices is synchronized by a common clock, thus as one bit/byte is sent out from A to B. • Another variation of synchronous communication is when two units are quite apart, they are driven by individual clocks but these clocks are synchronized. • In Asynchronous Communication the transmission and reception are not synchronized. • A device can send its own and other device may receive it. In this case byte is enveloped in a data frame will have Start bit stop bit parity bit • The baud rate data transmission speed in terms per second also must be predefined. KNCET EEE DEPARTMENT
- 4. • Serial data transfer in bit from received to parallel data in byte form for storage and processing. • Parallel data in memory to serial data ready to be transmitted • Such devices working in asynchronous mode are called USART. • The 8051 has on chip for serial communication. • RXD • TXD Serial Communication Modes • MODE 0 • MODE 1 • MODE 2 • MODE 3 KNCET EEE DEPARTMENT
- 6. MODE 0: • Data is transmitted as well as received through the RxD pin. • The shift clock is supplied through the TxD pin. • 8 bits of data are transmitted and received. • The LSB is transmitted first and similarly while receiving. • The baud rate is 1/12 of a oscillator frequency. • Transmit Interrupt flag (TI) is set when data bytes are transmitted and Receive Interrupt(RI) flag is set after receiving bits. • The TI and RI flags are noting but SCON register. This mode corresponds to SM0=0 and SM1=0. KNCET EEE DEPARTMENT
- 7. MODE 1: • Data is sent through the TxD pin and received through the RxD pin. A 10 bit frame containing 8 bit data (SM0=0), a start bit (=0) and a stop bit (=1) are used. • Thus there is a clear demarcation between end of one data frame and start of another data frame, once the stop bit is received. • The Stop bit is loaded into a bit cell RB8 in the SCON register. • As mode 0 here also an interrupt is generated once all the bit frames are received or transmitted. • Baud rate varies here the baud rate varied by changing preset count in the Timer1. • The start bit and stop bit are automatically added by the hardware by transmitting data. KNCET EEE DEPARTMENT
- 8. MODE 2: • 11 bits are transmitted or received. This 11 bit frame is specified as: 1 bit for start 8 bits for data 1 bit can be programmed 1 bit for stop bit • The 9 data bit programmable. This bit TB8 bit in SCON register, this is effectively used while transmitting data. • With little software overhead, this bits can be used to send the parity of the byte that is to be transmitted. • Transmitting: If we want to use 9 th bit as a parity we must load the TB8 with the parity of the byte that is to be transmitted. ACC has the byte to be transmitted. • Receiving: on reception of frame the 9 th bit goes to RB8 of the SCON register. The stop bit is ignored the baud rate in this mode is programmable either 1/32 or 1/64 of the oscillator frequency By making SMOD = 0 baud rate can be set to 1/64 of oscillator frequency, SMOD = 1 baud rate can be set to 1/32 of oscillator frequency. SMOD is 7 th bit PCON after SFR. KNCET EEE DEPARTMENT
- 9. MODE 3: • This mode is same as the mode 2 expect for baud rate. • Here the baud rate is variable as in case of mode 1. • The baud rate depends on overflow rate of timer 1. • By changing preset count in Timer 1 baud rate can be varied. Baud rate calculation = Timer 1 overflow rate n Where n is an integer and its value is either 32 or 16 If SMOD = 1 then n =16 else n = 32 Overflow rate = rate at which the counting in done /256-TH1 KNCET EEE DEPARTMENT
- 11. PCON • Power control register through which certain power control functions in CMOS version of the 8051 implemented. • In the HMOS version all the bits of PCON except 7 bit are dummy. • Bit 7 is SMOD and is used in both CMOS and HMOS versions to double baud rate in mode 1,2 and 3. • PCON is not bit addressable. KNCET EEE DEPARTMENT