Revised: Aug 1, 2003 1
EE4390
Microprocessors
Lessons 9, 10
Serial Communications Interface
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Microprocessors: Serial Communications Interface (SCI) - Lessons 9, 10, Study notes of Microprocessors
An overview of the serial communications interface (sci) in microprocessors, covering fundamentals and terminology, signals, multiple serial interfaces, sci transmitter, receiver, and registers. It also includes an example of initializing the sci system and a brief explanation of the rs-232 standard.
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Revised: Aug 1, 2003
EE
Microprocessors
Lessons 9, 10
Serial Communications Interface
Revised: Aug 1, 2003
Overview
-^ Fundamentals and Terminology•^ Signals•^ Multiple Serial Interface•^ Serial Communications Interface (SCI) - Transmitter– Receiver– Registers -^ SCI Programming•^ RS-232 interface
Revised: Aug 1, 2003
Fundamentals and Terminology (cont)• ASCII - American Standard Code for Information Interchange
"Copyright of Motorola, Used by Permission"
Revised: Aug 1, 2003
Fundamentals and Terminology (cont)• Parity bit - used to detect a single error– odd parity: odd number of ones in character– even parity: even number of ones in character• Simplex: transmit or receive data, notsimultaneously
Revised: Aug 1, 2003
Serial Communications Interface (SCI)
Transmitter
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Serial Communications Interface (SCI)
Receiver
Revised: Aug 1, 2003
SCI Baud Rate Control Registers
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SCI Data Registers High/Low
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SCI Programming
- Revised: Aug 1,
- SCI Control Registers 1,
- Revised: Aug 1,
- SCI Status Registers 1,
- Revised: Aug 1,
- Example (cont) SC1BDH, SC1BDL: SC1BDH = $00SC1BDL = $34 SC1CR1: M=0, (1 start, 1 stop,8 data bits) SC1CR2: TE =
Revised: Aug 1, 2003
Example (cont)
;SCI Initialization Example;Assume M = 8 MHz, 9600 BAUD;define register locations and masksSC1BDH = $00C
; Baud Register High location
SC1BDL = $00C
; Baud Register Low location
BAUD_HI = $
; Baud Register High mask
BAUD_LOW = $
; Baud Register Low mask
SC1CR1 = $00CA
; Control Register 1 location
SC1_CONT = $
; Control Register 1 mask
SC1CR2 = $00CB
; Control Register 2 location
SC1_MASK = $
; Control Register 2 mask
SC1SR1 = $00CC
; Status Register 1 location
SC1DRL = $00CF
; Data Register Low location
Revised: Aug 1, 2003
Example (cont)
;sci_init: initializes SCI system;Assume M = 8 MHz, 9600 BAUDsci_init:: LDAA
#BAUD_LOW
;set BAUD rate
STAA
SC1BDL
LDAA
#BAUD_HI
STAA
SC1BDH
LDAA
#SCI_CONT
;set MODE
STAA
SC1CR
LDAA
#SC1_MASK
;enable transmitter
STAA
SC1CR
LDAA
SC1SR
;clear TDRE bit - 2 step process
STAA
SC1DRL
;1: read SC1SR1, write SC1DRL
RTS^
;return from subsroutine
Revised: Aug 1, 2003
RS-232 Standard
-^ Electronic Industry Association (EIA) Standard•^ Evolved from 1960 standard - EIA-232-D•^ Four aspects: -^ Electrical specifications: voltage level, rise time, fall time–^ Functional specifications of each signal–^ Mechanical specifications: number of pins, connector shape,connector dimension–^ Procedural specifications -^ RS-232 voltage levels+12V0V -12V
idle^
idle
start^
data^
stop parity