lecture11 - 0306-250 Assembly Language Programming Lecture...

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Unformatted text preview: 0306-250 Assembly Language Programming Lecture Eleven: SCI Polled Receive •Polled Receive Algorithm •GetChar Subroutine • • • • SCI Registers Baud rate control registers (SCIBDH, SCIBDL) Control registers (SCICR1 , SCICR2) Status registers (SCISR1 , SCISR2 Data registers (SCIDRH, SCIDRL) – Read: Receive data register – Write: Transmit data register Serial Communications Interface (S12SCIV2) Block Description, p. 4. Two separate registers, which map to the same address 2 SCI0 Initialization • Set SCI0 baud rate SCI0BDH, SCI0BDL • Set SCI0 operation/format SCI0CR1 • Set SCI0 operation/enable SCI0CR2 Required once in program before any SCI operation 3 Program SCI Initialization (only once per program) • EQUates constants—at beginning of program SCI_9600H: SCI_9600L: SCI_8N: EQU EQU EQU $00 $0D %00000000 • Set SCI baud rate movb movb #SCI_9600H,SCI0BDH #SCI_9600L,SCI0BDL • Set SCI character format for serial bit stream movb #SER_8N,SCI0CR1 • Enable SCI transmitter and receiver movb #(mSCI0CR2_RE|mSCI0CR2_TE),SCI0CR2 4 Polled Receive What does it mean? • Poll – Question or canvas – Test • Receive – Acquire – Get HCS12-SCI application • Poll RDRF bit of SCI’s status register until SCI has received data RDRF = 1 • Read data received, from RDR www.m-w.com 5 Include File EQUates for SCI SR1 INCLUDE 'mc9s12dt256b.inc‘ ;*** SCI0SR1 - SCI 0 Status Register 1; 0x000000CC *** SCI0SR1: equ $000000CC ; bit numbers SCI0SR1_PF: SCI0SR1_FE: SCI0SR1_NF: SCI0SR1_OR: SCI0SR1_IDLE: SCI0SR1_RDRF: SCI0SR1_TC: SCI0SR1_TDRE: equ equ equ equ equ equ equ equ ; bit position masks mSCI0SR1_PF: equ mSCI0SR1_FE: equ mSCI0SR1_NF: equ mSCI0SR1_OR: equ mSCI0SR1_IDLE: equ mSCI0SR1_RDRF: equ mSCI0SR1_TC: equ mSCI0SR1_TDRE: equ 0 1 2 3 4 5 6 7 ; ; ; ; ; ; ; ; Parity Error Flag Framing Error Flag Noise Flag Overrun Flag Idle Line Flag Receive Data Register Full Flag Transmit Complete Flag Transmit Data Register Empty Flag %00000001 %00000010 %00000100 %00001000 %00010000 %00100000 %01000000 %10000000 6 ACIA Polled Receive Algorithm • Algorithm repeat { check RDRF bit of SCI SR } until (RDRF = 1) get character received, from SCI RDR • Note: to clear RDRF condition 1.Read SCI SR containing RDRF 2.Read from SCI RDR (must occur in this order) 7 Polled Receive Code • Algorithm repeat { check RDRF bit of SCI SR } until (RDRF = 1) get character received, from SCI RDR • Instructions—core of GetChar subroutine ; Poll RDRF until ready PollRx: ldaa SCI0SR1 anda #mSCI0SR1_RDRF beq PollRx ; Get character ldab SCI0DRL 8 ...
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