Unit 10 - Part 3

Address Selects Receiver

AddressCharacter

N Character Message

XMTR

RCVR RCVR RCVR RCVR……..

Receivers are put in “standby” mode by setting RWU (Receiver Wake Up) = 1

Receiver Wake Up

• If RWU == “1” (Receiver is in ‘stand-by’ state)

– If WAKE == “1” (Address Mark Wakeup)• A logic 1 in the msb position of a frame clears the RWU bit

and wakes up the SCI. (The logic 1 marks the frame as an address frame.)

» If Address matches, then Receive Message» If Address doesn’t match, then set RWU=“1”

– If WAKE == “0” (Idle line Wakeup)• An idle condition on the input clears the RWU bit and wakes

up the SCI. The next frame that is received is assume to contain an Address

– If Address matches, then Receive Message– If Address doesn’t match, then set RWU=“1”

RWU = “1”, WAKE = “0”

FrameN+1

Characters

FrameN+1

Characters

FrameN+1

Characters

Line Idle

• Enable Receiver when receiver input is in Idle state (when 10 or 11 1’s are received)• Next received character is considered an Address• If Address matches then receive the rest of Frame• If Address doesn’t match, set RWU = ”1” to ignore rest of Frame

RWU = “1” WAKE = “1”

• Received “wakes up” if Most Significant Bit of Received Character = “1”– 1 in MSB: Character is an Address– Receive Address

• If Match, receive remainder of frame• If No Match, set RWU back to “1” and ignore

remainder of frame

Single Wire Mode

• Loops = “1”, RSRC = “1”– TxDIR = “0” -- TxData is Input to Receiver– TxDIR = “1” -- TxData is Transmitter Output

XMTR

RCVR

TxDIR = “1”

TxDIR = “0”

Single WireHalf Duplex

TxD pin

SCI Interrupts

• 4 Sources of Interrupts on SCI– TDRE = “1” – Transmitter SCI Buffer Empty– TC = “1” – Transmitter Finished– RDRF = “1” – Receiver SCI Buffer Full– IDLE = “1” – Receive Line is Idle

• TDRE and RDRF are commonly used

• TC and IDLE used in special applications

SCI Interrupt Processingvoid sci0_isr(void){// SCI Interrupt has occurred, determine reason if((SCI0SR1&0x20)!=0) { // RDRF=“1” was source of interrupt, buffer is full c=SCI0DRL; // Read character to empty buffer ---- // handle the character } if((SCI0SR1&0x80)!=0) { // TDRE=“1” was source of interrupt, buffer is empty // Case 1 – If have a character c to transmit SCI0DRL = c; // Write character to full buffer } else {// Case 2 – No character to transmit SCI0CR2 = SCI0CR2&0x7F; // set TIE=“0” to disable transmitter interrupts } ---- ----}