ECE251: Thursday November 8

Transcription

1 ECE251: Thursday November 8 Universal Asynchronous Receiver & Transmitter Text Chapter 22, Sections read carefully TM4C Data Sheet Section 14-no need to read this A key topic but not a lab HW #7 due one week; Homework #8 due Nov. 29 Lab #8 this week and next; due week of Nov 26 Lab #9 week of Nov. 26; due week of Dec. 3 Practical #2 is week of Dec. 3 in lab. Final Exam on Monday, Dec 10, 2:00 p.m. Lecture #24 1

2 Types of Serial Communications Simplex--1 wire, 1 direction (TV, Radio, etc.) Half-Duplex--1 wire, 2 directions (Telephone) Line is switched: Protocol to determine how switched Full-Duplex--2 wires, 2 simultaneous directions Lecture #24 2

3 What does UART Mean? Universal UART is programmable. Asynchronous Sender provides NO clock signal to receivers Receive & Transmit Lecture #24 3

4 Serial Communication Terminology Clock: Defines the rate of data transfers (in Hz) Bit rate: The number of bits transmitted per second. It equals the clock signal rate (in bits/sec vs Hz) Bit time: Reciprocal of bit rate (sec) i.e. bit period Baud: Unit of bits transmitted per second. Baud = bits/sec. NRZ line code: Non-Return to Zero. Line Code describes the format used to transfer each information bit NRZ: The bit (1 or 0) is place on the transmission line for the entire bit cell: e.g.: Serial bit stream Bit data MODEM: MOdulator/DEModulator Used to turn digital signals into audio (telephone) signals and viceversa. Lecture #24 4

5 Serial Communication Terminology ASCII: American Standard Code for Information Interchange 7 bit code--all numbers + upper/lower case characters + many more E.g. h = $68 D = $44? = $3F = $20 See Appendix C on Lab page Parity Bit: Additional bit (usually most significant bit) used to detect a single error in a sequence of bits Typically done at character level: Use 8 bits to send a 7 bit ASCII character + parity May be Odd (extra bit makes entire sequence have odd # of ones) or may be Even (extra bit makes entire sequence have even # of ones) Example: What is D in an Odd Parity transmission? In Even? $44 = 2_ _ = $C4 odd $44 = 2_ _ = $44 even Lecture #24 5

6 Serial Communication Standards RS-232: Historically the most common asynchronous standard Established in 1960 By Electronic Industry Association (EIA) for interfacing between a computer and a modem. Revised in 1991and renamed: EIA-232-E. Still called RS-232. Computers and Terminals are Data Terminal Equipment Modems, Bridges, Routers, etc. are Data Communications Equipment Four aspects of standard Electrical--voltage levels, rise times, fall times, data rates, distances, Functional--function of signals Mechanical--# of pins, shape/dimensions of connectors Procedural--sequence of events for transmitting data Data Terminal Equipment Data Communications Equipment Lecture #24 6

7 Down and Dirty with RS-232 Signal levels: (large, ugly" voltages) 0 --between +3 and +25 v. (Typically +12 v) 1 --between -3 and -25 v. (Typically -12 v) Signal format: Start and Stop bit used to Synchronize signals Idle (high) Start bit 8-bit ASCII Code (least significant first) Stop bit 1 frame ~ 10 bit times Receiver must have a clock running at 16X the transmitter s bit rate. At 28,800 baud, how long does it take to send TM4C12, including start and stop bits? What speed is the internal receiver clock? 6 char. x 10 bits/char 28,800 bits/sec = msec for 6 chars 28.8 KHz*16 = 460 KHz receiver clock frequency Lecture #24 7

8 UART Hardware UART = Universal Asynchronous Receiver/Transmitter It s the hardware (IC components in our processor/i/o subsystem) that is used to handle the asynchronous communications, at the heart of a modem s or computer s serial communication functionality. It performs Parallel Serial (transmit) and Serial Parallel (receive) conversion. See ECE102 It has a sophisticated programmable clock generator to handle multiple data frequencies very accurately. It often has a multi-byte buffer to reduce frequency of CPU interrupts to transfer more data. Lecture #24 8

9 TM4C UART Capability 8 Separate UART systems on chip Half-duplex operation can do both transmit and receive, but not at same time FIFO Buffers NRZ (Non-Return-to-Zero) signal format. Baud rate selection using baud rate registers. Programmable 5 to 8 data bit (excluding parity) format. Interrupt generation capability. Receiver noise error detection. Framing error detection (If stop bit is not detected). Transmitter parity creation and receiver parity error detection. Lecture #24 9

10 UART Block Diagram Lecture #24 10

11 UART Character Frame from TM4C Data Sheet n is the TM4C UART number: 0-7 Lecture #24 11

12 Details of Character Frame Always a logic 0 One Start bit May be a logic 0 or 1 Always a logic 1 One or more Stop bits 7 bits plus parity 8 bits plus parity Least significant bit first Parity bit last Lecture #24 12

13 Transmitting Bytes 0x32 and 0x3C 104µsec 1 start bit, 1 stop bit, 8 data bits, no parity, baud rate = 9.6 Kbaud How would this change with even parity? With odd parity? With 7 data bits no parity? With even parity? With odd parity? With 2 stop bits? Can these transmissions represent ASCII? Lecture #24 13

14 UART Synchronization Understand this concept! IDLE SIGNAL-Stop Bit START Bit ECE102 State Machine Lecture #24 14

15 Practice with RS-232 Signals µsec time What is the Baud rate? If I told you there are 7-8 data bits & one stop bit per frame, with one starting on left side of slide, how many frames are being sent? Can you tell if this is 8 bits of data vs. 7 bits of data + parity If it s 7 bits of data + parity, what IS the parity So, can you tell which by looking at this chart? If it is 7 bits + parity, can it represent ASCII? If so, what ASCII characters are being transmitted? If it is 8 bits without parity, what are the bytes being transmitted (in time order)? From end of first stop bit to end of last stop bit above, how long does this transmission take? Other questions about this? Lecture #24 15

16 Practice with RS-232 Signals µsec time What is the Baud rate? If I told you there are 7-8 data bits & one stop bit per frame, with one starting on left side of slide, how many frames are being sent? Can you tell if this is 8 bits of data vs. 7 bits of data + parity If it s 7 bits of data + parity, what IS the parity So, can you tell which by looking at this chart? If it is 7 bits + parity, can it represent ASCII? If so, what ASCII characters are being transmitted? If it is 8 bits without parity, what are the bytes being transmitted (in time order)? From end of first stop bit to end of last stop bit above, how long does this transmission take? Other questions about this? Lecture #24 16

17 Practice with RS-232 Signals µsec time What is the Baud rate? If I told you there are 7-8 data bits & one stop bit per frame, with one starting on left side of slide, how many frames are being sent? Can you tell if this is 8 bits of data vs. 7 bits of data + parity If it s 7 bits of data + parity, what IS the parity So, can you tell which by looking at this chart? If it is 7 bits + parity, can it represent ASCII? If so, what ASCII characters are being transmitted? If it is 8 bits without parity, what are the bytes being transmitted (in time order)? From end of first stop bit to end of last stop bit above, how long does this transmission take? Other questions about this? Lecture #24 17

18 Practice with RS-232 Signals µsec time What is the Baud rate? If I told you there are 7-8 data bits & one stop bit per frame, with one starting on left side of slide, how many frames are being sent? Can you tell if this is 8 bits of data vs. 7 bits of data + parity If it s 7 bits of data + parity, what IS the parity So, can you tell which by looking at this chart? If it is 7 bits + parity, can it represent ASCII? If so, what ASCII characters are being transmitted? If it is 8 bits without parity, what are the bytes being transmitted (in time order)? From end of first stop bit to end of last stop bit above, how long does this transmission take? Other questions about this? Lecture #24 18

19 More Practice with RS-232 bit cell time Suppose baud rate is 9.6 Kbaud/sec with one stop bit per frame and 7-8 data bits How long is a bit cell? Use correct engineering units! What else can you tell me about this specific signal? Lecture #24 19

20 Even More Practice bit cell time We want to send 2Pi at 4.8Kbaud rate, using one stop bit per frame with even parity. What is the bit cell width? Show the signal above What clock rate should the receiver be using to decode this signal? OK! Do you understand RS-232 signals well enough for a similar question on the final exam? Good chance there will be one! Lecture #24 20

21 TM4C UART Interfaces External Interfaces Each module uses two signal pins (n is module number 0-7) UnRX receives data UnTX transmits data These pins are alternate functions for GPIO pins (next slide) UART supports hardware parity for transmit and receive When enabled, parity bit is generated for transmitted data and computed/compared for received data. Received parity errors are flagged in hardware and can generate interrupts. UART Baud Rate Generator Uses Bus Clock or Precision Clock See slides from next lecture for more details and examples Lecture #24 21

22 UART Signals GPIO pins used for UART Signals AFSEL Register set to specify something other than GPIO function Which other function? PMCn field of GPIO PCTL register assigns UART signal to the specified GPIO Port pin see next slide Lecture #24 22

23 UART Alternate Function Select - Review Alternate function selected as in Timer Module: Uses GPIO DIR, AFSEL, PCTL, and AMSEL for particular port to be used Clear DIR register bits corresponding to input pins and set DIR register pins corresponding to output pins (0 thru 7 for both) Enable alternate function in AFSEL register for port to be used and for the 2 bits corresponding to pins using as Rx and Tx In Register PCTL for port to be used, set appropriate bits (4 per pin) to choose UART (value 1). E.g. for U3Rx, which uses PC6, set bits 27:24 of GPIO_PORTC_PCTL to 0x01 Disable analog for both Rx and Tx pins by clearing corresponding bits of AMSEL register for the port to be used. See Timer Module Lecture for a complete example Do you need to remember all this? NO. Just know where to find it! Lecture #24 23

24 More on UART Next Lecture UART Signal Review Baud Rate Generation TM4C Registers TM4C Setup and Operation USB Section 22.4 of text Chapter 18 of TM4C Data Sheet NOT an exam question Lecture #24 24