ECE 4510/5530 Microcontroller Applications Week 10

Transcription

1 ECE 4510/5530 Microcontroller Applications Week 10 Dr. Bradley J. Bazuin Associate Professor Department of Electrical and Computer Engineering College of Engineering and Applied Sciences

2 Lab 9 & 10 Elements Inter-Integrated Circuit (I2C) Interface SCL and SDA connections Calendar MCP7940M-I/P Real-Time Clock/Calendar PING ECE

3 Lab 8 Note: ADC Dynamic Range ECE 4510/5530 3

4 The True Range of and ADC V ADC values are readily defined for and N-bit converter ADC_integer _ InUnipolar 2.5 V _ In N 2 But what is really being measured? ECE 4510/ ADC_integer 2 Bipolar N 1 Voltage guard bands! you don t want to go all the way to 0.0V or 2.5V Example: Temperature indoor/outdoor -30 C to + 50 C or -22 F to 122 F With our device, the measurement range is -0.3V to + 0.5V Unipolar ADC range: decimal 0 to 13,107 or hex 0x0000 to 0x3333 Bipolar ADC range: decimal 28,836 to 39,322 or hex 0x70A4 to 0x999A We have lost over two bits of measurement precision! Only 20% of the measurement range is being used! 4

5 Tailoring ADCs to tasks: Options 1) Adjust the internal gain. The device we are using could use an internal gain of 4. The new measurement range would be to V 2) Provide external gain. Provide an analog op amp circuit so that the signal range nearly fills the ADC range (you still may only use 80% of the total) 3) Use a different Vref for the ADC A possible solution, but normally applying gain is preferred. The noise in the ADC has a defined voltage level. Measuring signals smaller than the noise voltage is not a good idea. ECE 4510/5530 Analog sensor signals are often buffered, had gain applied, filtered, or otherwise preconditioned before the ADC. DAC outputs may also be conditioned. 5

6 Lab 9: Real-Time Clock/Calendar ECE 4510/5530 6

7 I2C Real-Time Clock/Calendar MCP7940M Features Real-Time Clock/Calendar (RTCC): Hours, Minutes, Seconds, Day of Week, Day, Month and Year Dual alarm with single output On-Chip Digital Trimming/Calibration: Range -127 to +127 ppm, Resolution 1 ppm Programmable Open-Drain Output Control: CLKOUT with 4 selectable frequencies Alarm output 64 Bytes SRAM Low-Power CMOS Technology: Dynamic Current: 400 A max write 100 khz and 400 khz Compatibility ESD Protection >4,000V Packages include 8-Lead SOIC, TSSOP, 2x3 TDFN, MSOP and PDIP Temperature Ranges: Industrial (I): -40 C to +85 C

8 Typical Application Schematic

9 MCP7940M Address Map Detail Same as textbook Extra bits Matches clock structure Matches clock structure

10 MCP7940M Control Register Bit 7 is the OUT bit. This sets the logic level on the MFP when not using this as a square wave output. (prefer high for potential interrupt signals = 1) Bit 6 is the SQWE bit. Setting this bit enables the divided output from the crystal oscillator.(we wish to use the signal as an alarm interrupt = 0) Bits 5:4 determine which alarms are active. (set according to requirement) 00 No Alarms are active 01 Alarm 0 is active 10 Alarm 1 is active 11 Both Alarms are active Initial test: 0x40 (1 Hz output) Alarms: 0x80, 0x90, 0xA0 or 0xB0 (high output going low alarm condition) Bit 3 is the EXTOSC enable bit. Setting this bit will allow an external khz signal to drive the RTCC registers, eliminating the need for an external crystal. (set to 0) Bit 2:0 sets the internal divider for the khz oscillator to be driven to the MFP. The duty cycle is 50%. The output is responsive to the Calibration register. The following frequencies are available: (typically 000) Hz khz khz khz 1xx enables the Cal output function. Cal output appears on MFP if SQWE is set (64 Hz Nominal). See Section Calibration for more details.

11 MCP7940M Alarms 0x07h Is the Control register. Bits 5:4 determine which alarms are active. ALMxPOL = 0 00 No Alarms are active 01 Alarm 0 is active ALMxC2 = Alarm 1 is active 11 Both Alarms are active Locations 0x0Dh and 0x14h have additional bits for alarm configuration. ALMxPOL: This bit specifies the level that the MFP will drive when the alarm is triggered. ALM2POL is a copy of ALM1POL. The default state of the MFP when used for alarms is the inverse of ALM1POL. ALMxIF: This is the Alarm Interrupt Fag. This bit is set in hardware if the alarm was triggered. The bit is cleared in software. ALMxC2:0: These Configuration bits determine the alarm match. The logic will trigger the alarm based on one of the following match conditions 000 Seconds match 001 Minutes match 010 Hours match (takes into account 12/24 hour) 011 Matches the current day, interrupt at a.m. 100 Date 111 Seconds, Minutes, Hour, Day, Date, Month

12 MCP7940M I2C Data Transfer MCP7940M supports both 100 khz and 400 khz data transfer. The device address (ID) of the MCP7940M is

13 Lalith s Example Code I2C routines i2c.h and i2c.c // Function prototypes int I2Cinit (char baud_divisor, char dev_id); int I2Cstart (char); int I2Crestart (char); int I2Cwritec (char data); int I2Cwritestr (char *,int); char I2Creadc_ack (void); char I2Creadc_nack (void); int I2Creadstr (char *,int); // uses special definitions for I2C_STOP IBCR I2C_TX_ACK IBCR I2C_TX_NACK IBCR I2C_ACK_CHK(x) Real Time Clock/Calendar rtic.h and rtic.c // Function prototypes int RTICinit (void); int RTICwrite (char,char); char RTICread (char); int RTICpwm (void); //global declaration externs

14 Day of Week from Month/Day/Year The Day of the Week can be determined based on knowing the day, month and year. Microchip Application Note AN1303 Software Real-Time Clock and Calendar Using PIC16F Add a century offset (6 for ) Add the two digits of the year (13 for 2013) Add the number of leap years since 2000 ( int(13/4) = 3) Add a month offset based on a table of values (March = 3) Add the Date (22 March 2013) Take the modulo 7 of the sum ( = 47 5) With Sunday as 0 compute the day. (5 Friday) ECE 4510/

15 Lab 10: see PING Notes ECE 4510/