AN1759 Freescale Semiconductor, Inc. Non-Volatile Clock MC68
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AN1759
Freescale Semiconductor, Inc.
Non-Volatile Clock MC68HC705J1A
Mark Glenewinkel Field Applications Engineering Consumer Systems Group Austin, Texas
Introduction
Many embedded systems require measurement time. This accomplished internally some MCUs that have on-chip real-time clocks. Even date, month, leap year measurement, this task take substantial amounts bandwidth code space. DS1307 64x8 serial real-time clock provides calendar time keeping functions along with system-enhancing non-volatile RAM. With 2-wire interface, timekeeping managed easily. Some applications using DS1307 are: Logging chronological events Tracking power down time system Providing alarm functions
Motorola, Inc., 1998
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Freescale Semiconductor, Inc. Application Note
non-volatile (random-access memory) also gives user additional applications such Power down information storage consumer electronics like TVs, VCRs, hand-held portables Identification number storage remote addressing security Storage telecommunication information like phone number recall speed dialing
Freescale Semiconductor, Inc.
This application note describes interface between MC68HC705J1A (J1A) DS1307. Circuitry example code given demonstrate interface between parts.
Features
DS1307 provides these features: Real-time clock counts seconds, minutes, hours, week, date, month, year. Leap year compensation valid 2100 bytes non-volatile data storage 2-wire serial interface Programmable square wave output with frequencies 4.096 kHz, 8.192 kHz, 32.768 Automatic power switching battery when main power fails battery backup mode, less than consumed 8-pin SOIC package Optional industrial temperature range
Description
DS1307 low-power binary coded decimal (BCD) clock calendar that provides seconds, minutes, hours, day, date, month, year. addition, bytes non-volatile RAM. End-of-the-month adjustments automatic months with less than days. device also corrects leap years. clock operate either 12-hour 24-hour mode. 12-hour mode, a.m./p.m indicator used.
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MOTOROLA
Application Note DS1307 Hardware Interface
DS1307 built-in power management circuitry detect power failures when detected will switch power over battery back-up pin, VBAT. Access device terminated when falls below 1.25 VBAT. Further accesses device allowed. power device switches power from VBAT when volts above VBAT. Once higher than 1.25 VBAT, normal operations continue. Address data communicated 2-wire bus. DS1307 operates slave times accessed first transmitting DS1307's identification code bus.
Freescale Semiconductor, Inc.
DS1307 Hardware Interface
Pinout Descriptions
VBAT
SQW/OUT
Figure DS1307 Pinout These pins serve main power source device. When volts applied this pin, device fully accessible data read written. power falls below 1.25 VDD, device switches power supply VBAT. this point, reading writing device prohibited. timekeeping function nonvolatile unaffected. This power input standard 3-volt lithium battery other 3-volt source. proper operation, this voltage must held between volts. lithium battery with least 35-mA hours rating will back DS1307 more than years absence power.
VBAT
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Freescale Semiconductor, Inc. Application Note
These pins used connect 32.768-kHz crystal device. other capacitors resistors needed this crystal circuit. internal oscillator circuitry designed crystal with load capacitance 12.5 test circuit described this application note, Epson C-001R crystal used. Digi-key part number this device SE3201-ND. When enabled, this outputs four selectable frequencies: 4.096 8.192 32.768
SQW/OUT
Freescale Semiconductor, Inc.
1-Hz signal used feed external interrupt MCU. This allows minimal bandwidth when servicing timekeeping function system. When disabled, acts normal output pin. controlled DS1307 control register. clock input DS1307 2-wire serial interface. used transmit receive data 2-wire serial interface. open-drain that requires external pullup resistor.
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Application Note DS1307 Hardware Interface
Block Diagram
VBAT POWER CONTROL REAL-TIME CLOCK
OSCILLATOR DIVIDER
SQW/OUT
SQUARE WAVE CONTROL LOGIC
Freescale Semiconductor, Inc.
SERIAL INTERFACE
ADDRESS REGISTER
Figure DS1307 Block Diagram Serial Interface DS1307 supports bidirectional, 2-wire protocol. protocol these characteristics: device sending data defined transmitter. device receiving data defined receiver. device controlling transfer called master. device being controlled called slave. master initiates transactions. master always provides clock both transmit receive operations. DS1307 always considered slave. clock signal called SCL. data signal called SDA. data sent most significant (MSB) first.
Figure shows 2-wire interface between master slave.
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Freescale Semiconductor, Inc. Application Note
MASTER PORT DIRECTION DS1307 2-WIRE PORT
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Figure 2-Wire Serial Interface Idle Start Transfer idle mode, both held high. transfers begin with start transfer condition. This done bringing from HIGH while HIGH. DS1307 monitoring this signal will start transactions until this condition met. Figure transfers must terminated with stop transfer condition. This done bringing from HIGH while HIGH. stop transfer used only after transmitting device releases bus. Figure
Stop Transfer
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Application Note DS1307 Hardware Interface
START
STOP
Figure Start Stop Transfer Timing
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Data Transfer
Data transmitted rising edge SCL. Data only changed while LOW. receiving device samples after goes HIGH. There clock pulse data transmitted. Figure
DATA STABLE DATA CHANGE DATA STABLE
Figure Data Transfer Timing Acknowledge Transfer acknowledge transfer type handshaking convention used signify that successful transfer data taken place. After transmitting device sends eighth byte data, releases bus. master sends ninth clock signal receiver acknowledges transfer pulling LOW. Once transmitter reads condition SDA, proceeds taking over sending next byte data. DS1307 transmitting data master wants further transmissions, master sends signal (HIGH) back DS1307. This tells DS1307 that more transfers needed stop transfer condition will initiated soon. Figure these different timing patterns.
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Freescale Semiconductor, Inc. Application Note
FROM SLAVE
FROM MASTER
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LAST RECEIVE, HIGH
Figure Acknowledge Timing 2-Wire Protocol Example example protocol needed write address DS1307 master transmits start transfer. master transmits DS1307 7-bit identification code, %1101000. Since this data write transfer, master then transmits Since byte just been transmitted, receiver (DS1307) will send acknowledge transfer. master reads LOW. master sends address DS1307 receives back acknowledge. master sends data, $10, DS1307 receives back acknowledge. DS1307 writes address $07. Finally, stop transfer sent DS1307 complete transaction.
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Application Note DS1307 Software Interface
DS1307 Software Interface
Memory
DS1307's memory shown Figure real-time clock registers located address locations $07. bytes non-volatile located address locations $3F. During multibyte addresses, address pointer wraps around after reaches $3F.
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SECONDS MINUTES HOURS DATE MONTH YEAR CONTROL
56X8
Figure DS1307 Memory Register real-time clock registers shown detail Figure time calendar writing appropriate registers. information binary coded decimal (BCD) format. enable processor, write CLOCK HALT register $00. DS1307 shipped with this Either 12-hour 24-hour clock format used. register device 24-hour mode. Likewise, when device 12-hour mode. address used second
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Freescale Semiconductor, Inc. Application Note
hours when 24-hour mode. When using 12-hour mode, p.m. a.m.
CLOCK HALT SECONDS MINUTES SECONDS MINUTES HOURS DATE MONTH YEAR SQWE
Freescale Semiconductor, Inc.
DATE MONTH
YEAR
Figure DS1307 Register Control Register control register used control SQW/OUT pin. Controls output level SQW/OUT when SQWE SQW/OUT HIGH SQW/OUT SQWE Enables oscillator square wave SQW/OUT Square wave enabled Square wave disabled Square wave output frequency 4.096 8.192 32.768
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Application Note DS1307 Software Interface
Data Write Sequence
first byte transmitted write DS1307 7-bit identification code followed bit. writes, this will next byte transmitted DS1307 address pointer. After this, bytes data written DS1307 transmitted. After each byte data written, address pointer incremented. Figure
DATA XXXX,XXXX DATA (N+?) XXXX,XXXX
START
DS1307 ADDRESSR/W ADDRESS POINTER 1101000 XXXX,XXXX
STOP
Freescale Semiconductor, Inc.
Figure Data Write Sequence
Data Read Sequence
first byte transmitted read from DS1307 7-bit identification code followed bit. reads, this will Then DS1307 will begin transmitting data back master. long DS1307 receives clocks acknowledgments, keeps transmitting data. starting address previous address pointer from last write transaction. needed, write sequence with only address used initialize address pointer reads.
NOTE:
Remember that last byte read, master sends back DS1307.
DATA XXXX,XXXX DATA (N+?) XXXX,XXXX STOP
DS1307 ADDRESS START 1101000
Figure Data Read Sequence
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Freescale Semiconductor, Inc. Application Note MC68HC705J1A Hardware Interface
With only pins, smallest members HC05 Family. total 1240 bytes erasable programmable read-only memory (EPROM) includes (input/output) pins. schematic used testing DS1307 interface MMEVS development system shown Figure pins used drive DS1307 listed here also.
Freescale Semiconductor, Inc.
Port This (SCL) configured output drive serial clock pin, SCL, DS1307. Port This (SDA) used transmit receive data DS1307.
further information HC705J1A, consult MC68HC705J1A Technical Databook (MC68HC705J1A/D).
EPSON #C-301R 32.768-kHZ XTAL
DS1307
SQW/OUT VBAT
BATTERY MMEVS INTERFACE
Figure J1A-to DS1307 Interface Test Circuit
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Application Note MC68HC705J1A Software Interface
MC68HC705J1A Software Interface
driving manipulation process toggling pins with software instructions create certain hardware peripheral. HC05 provides special instructions specifically manipulate single pins. Five subroutines were created provide easy application programming interface (API). These routines are:
Freescale Semiconductor, Inc.
START_SER Sends start condition STOP_SER Sends stop condition master takes contents AccA transmits first DS1307. master also checks acknowledgement from DS1307. After master addresses DS1307 with identification code read bit, DS1307 transmits byte data back master. This routine reads that byte puts into AccA. master also generates acknowledgment back DS1307. RXD_LAST This routine just like used last byte read from DS1307. does generate acknowledgment back DS1307.
flowcharts DS1620 serial drivers shown Flowcharts Test Interface. These routines were written especially DS1307 able properly drive other peripherals with 2-wire serial buses. typical application would SQW/OUT DS1307. When configuring this 1-Hz signal, feed signal MCU. interrupt routine created read contents DS1307 every time 1-Hz signal hits pin. This should take minimal bandwidth provide user easy retrieve time date information. main test routine written verify interface between DS1307 J1A. writes known date time into DS1307
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Freescale Semiconductor, Inc. Application Note
then reads back out. data read into buffer HC05. When emulator stopped, read contents HC05 buffer verify transmission process. test routine sequence shown Figure assembly code test routine provided section titled Code Listing. sequence tests Configure device turn 1-Hz signal SQW/OUT pin. Transmit start condition. Transmit DS1307 code write device %11010000. Transmit control register address then $10.
Freescale Semiconductor, Inc.
Transmit stop condition. Write start time. Transmit start condition. Transmit DS1307 code write device %11010000. Transmit starting address $00, seconds register.
Transmit Saturday, June 1998, 4:30:00 p.m. writing seconds register, crystal circuit been turned on.) Transmit stop condition. Read time date, store away HC05 buffer. Transmit start condition. Transmit DS1307 code write device %11010000. Transmit starting address $00.
Transmit stop condition. Transmit start condition.
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Application Note Development Tools
Transmit DS1307 code read from device %11010001.
Read date time store away HC05 RAM. Transmit stop condition. Since real-time clock running, restart code step verify that keeping time. This routine demonstrates interface software needed communicate with DS1307. Although used, HC05 device could utilize this interface code. Minor adjustments port pins memory maps might necessary.
Freescale Semiconductor, Inc.
Development Tools
interface created tested using these development tools: M68MMPFB0508 Motorola MMEVS platform board X68EM05J1A Motorola emulation module Version 1.02 Editor, assembler, debugger Microcomputer Systems
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Freescale Semiconductor, Inc. Application Note Flowcharts Test Interface
START_SER
TAKE
TAKE
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RETURN FROM
STOP_SER
TAKE HIGH
TAKE HIGH
RETURN FROM
Figure START_SER STOP_SER Subroutines
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Application Note Flowcharts Test Interface
COUNTER
LEFT SHIFT ACCA, CARRY
MAKE INPUT
CARRY
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TOGGLE CLOCK SLAVE SENT
DECREMENT
MAKE OUTPUT RETURN FROM
LOOP DONE?
ERROR LOOP
Figure Subroutine
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Freescale Semiconductor, Inc. Application Note
RXD/RXD_LAST
MAKE INPUT
COUNTER
SCL=1
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CARRY
ROTATE LEFT ACCA PUTS CARRY INTO ACCA DECREMENT
YES, RECEIVED 8-BIT DATA MAKE OUTPUT TOGGLE CLOCK SCL=1 SCL=0 RETURN FROM WITH RXD_LAST WITH
Figure RXD/RXD_LAST Subroutines
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Application Note Flowcharts Test Interface
START
Config CONTROL Transmit START_SER DS1307_WRITE CONTROL Transmit STOP_SER
Freescale Semiconductor, Inc.
Write Start Time Transmit START_SER DS1307_WRITE SECONDS START_SECONDS START_MINUTES START_HOURS START_DAY START_DATE START_MONTH START_YEAR Transmit STOP_SER Read Time, store HC05 Transmit START_SER DS1307_WRITE SECONDS Transmit SER_STOP Transmit START_SER DS1307 store BUF_SECONDS store BUF_MINUTES store BUF_HOURS store BUF_DAY store BUF_DATE store BUF_MONTH RXD_LAST store BUF_YEAR Transmit SER_STOP
Infinite Loop
Figure Flowchart Main Test Routine
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Freescale Semiconductor, Inc. Application Note Code Listing
File name: DS1307.ASM Example Code MC68HC705J1A Interface Dallas DS1307 Serial Real Time Clock Ver: Date: June 1998 Author: Mark Glenewinkel Motorola Field Applications Consumer Systems Group Assembler: 1.02 code explanation flow charts, please consult Motorola Application Note "Add Non-volatile Clock MC68HC705J1A" Literature AN1759/D SYSTEM DEFINITIONS EQUATES Internal Register Definitions PORTA ;PortA DDRA ;data direction PortA Application SER_PORT DS1307_WRITE DS1307_READ SECONDS MINUTES HOURS DATE MONTH YEAR CONTROL Specific Definitions
Freescale Semiconductor, Inc.
;PORTA SER_PORT ;PORTA, clock signal ;PORTA, data signal ;addresses DS1307 write ;addresses DS1307 read ;DS1307 address seconds ;DS1307 address minutes ;DS1307 address hours ;DS1307 address ;DS1307 address date ;DS1307 address month ;DS1307 address year ;DS1307 address control
Memory Definitions EPROM $300 RESET $7FE
;start EPROM ;start ;vector reset
Time Start Definitions test Start Saturday, June 20th, 1998, 4:30:00 START_SECONDS seconds START_MINUTES minutes START_HOURS hours, Hour mode START_DAY ;Saturday START_DATE ;20th START_MONTH ;June START_YEAR ;1998
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Application Note Code Listing
VARIABLES Buffer test reading data from DS1307 BUF_SECONDS ;buffer HC05 seconds BUF_MINUTES ;buffer HC05 hours BUF_DAY ;buffer HC05 BUF_DATE ;buffer HC05 date BUF_MONTH ;buffer HC05 month BUF_YEAR ;buffer HC05 year MAIN ROUTINE EPROM ;start begining EPROM Intialize Ports START #$03 ;init SER_PORT SER_PORT #$03 ;make SER_PORT pins outputs DDRA DS1307 configuration Turn osc, turn SQW/OUT with signal START_SER ;start serial transmission #DS1307_WRITE #CONTROL #$10 STOP_SER ;address DS1307 device, write ;send address control ;send config data ;stop serial transmission ;start serial transmission ;address DS1307 device, write ;start address DS1307 ;write seconds ;write minutes ;write hours ;write ;write date ;write month ;write year ;stop serial transmission
Freescale Semiconductor, Inc.
Write Starting Time DS1307 START_SER #DS1307_WRITE #SECONDS #START_SECONDS #START_MINUTES #START_HOURS #START_DAY #START_DATE #START_MONTH #START_YEAR STOP_SER
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Freescale Semiconductor, Inc. Application Note
Read Time, store away HC05 time buffer verification Write starting address START_SER ;start serial transmission #DS1307_WRITE #SECONDS STOP_SER ;address DS1307 device, write ;start address DS1307 read ;stop serial transmission ;start serial transmission ;address DS1307 device, read ;read seconds, store buffer ;read minutes, store buffer ;read hours, store buffer ;read day, store buffer ;read date, store buffer ;read month, store buffer ;read year, store buffer ;stop serial transmission ;test sequence over
Read Time data HC05 buffer START_SER
Freescale Semiconductor, Inc.
DUMMY
#DS1307_READ BUF_SECOND BUF_MINUTES BUF_HOURS BUF_DAY BUF_DATE BUF_MONTH RXD_LAST BUF_YEAR STOP_SER DUMMY
SUBROUTINES Sends Start command START_SER bclr SDA,SER_PORT ;SDA=0 bclr SCL,SER_PORT ;SCL=0 Sends Stop command STOP_SER bset SCL,SER_PORT bset SDA,SER_PORT ;SCL=1 ;SDA=1
Routine takes contents AccA transmits serially DS1307, first Looks ACK, goes ERROR routine ;set counter WRITE asla bset bclr ;Carry SDA,SER_PORT CLOCK_IT SDA,SER_PORT ;SDA=1 ;branch clock_it ;SDA=0 ;evens
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Application Note Code Listing
bset bclr decx Check bclr bset brclr ACK_ERROR bclr bset
CLOCK_IT
SCL,SER_PORT SCL,SER_PORT WRITE SDA,DDRA SCL,SER_PORT SDA,SER_PORT,J2 ACK_ERROR SCL,SER_PORT SDA,DDRA
;SCL=1 ;SCL=0 ;decrement counter ;SDA input ;SCL=1 SDA=0, slave slave ACK, error loop ;SCL=0 ;SDA output ;return from
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Routine clocks contents Generates back bclr READ bset brclr rola bclr
DS1307 read data from SDA, first AccA slave SDA,DDRA ;make input ;set counter SCL,SER_PORT SDA,SER_PORT,J3 SCL,SER_PORT READ SDA,DDRA SDA,SER_PORT SCL,SER_PORT SCL,SER_PORT ;make output ;SDA=0 ;SCL=1 ;SCL=0 ;return from ;SCL=1 ;carry ;put carry into AccA ;SCL=0 ;decrement counter
decx back slave bset bclr bset bclr
Routine clocks DS1307 read data from SDA, first contents AccA Generates back slave, signals last read DS1307 RXD_LAST bclr SDA,DDRA ;make input ;set counter READ_LAST bset brclr rola bclr SCL,SER_PORT SDA,SER_PORT,J4 SCL,SER_PORT READ_LAST SDA,DDRA SDA,SER_PORT SCL,SER_PORT SCL,SER_PORT ;make output ;SDA=1 ;SCL=1 ;SCL=0 ;return from ;SCL=1 ;carry ;put carry into AccA ;SCL=0 ;decrement counter
decx back slave bset bset bset bclr
VECTOR TABLE RESET START
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Freescale Semiconductor, Inc. Application Note References
MC68HC705J1A Technical Data, Motorola document order number MC68HC705J1A/D, 1996. M68HC05 Applications Guide, Motorola document order number M68HC05AG/AD, 1996. DS1307 Datasheet, Dallas Semiconductor, 1997.
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