GCBASIC / Discussion / Help: DS1307 to MCP7490N

I am using a Microchip MCP7490N RTC. It's very similar to the Maxim DS1307, the main changes are that the I2C bus address is different, and you write 1 to bit 7 of 0x00 to start the oscillator instead of writing 0. There are some extra features as well such as alarms which can be set.

I'm using the DS1307.h library in GCB and I've modified it to include these changes and I am able to start the clock, set the time and read the time (I haven't gone any further yet).

One problem I am having though, is when I enable the oscillator it adds 48 seconds to the clock.
If I reset the clock (i.e. set everything to zero) and read the time it comes up with 00:00:00 as expected.
If I set the time to say 20:18:10 and read the time back it gives 20:18:10.
If I set the oscillator going, it will then read the time as 20:18:58 then continue running.

Does anyone know what's going on here? Did the same thing happen on a DS1307? Has anyone else used the MCP7490N with GCB?

This is the output of my LCD immediately after a power cycle (including of the MCP7940N) showing the values of initOsc and readReg as well as the clock value.
LCD

Extract of my MCP7940N.h (based on DS1307.h)

<font color="AA0000">
 ' This is the address of the generic MCP7940N
 #define MCP7940N_AddrWrite 0xDE
 #define MCP7940N_AddrRead 0xDF

 '  Define some useful memory locations
 #define MCP7940N_time 0x00     'Start of the time registers - 0x00
 #define MCP7940N_date 0x04     'Start of the date registers - 0x04
 #define MCP7940N_control 0x07      'Control register
 #define MCP7940N_alarm0 0x0A       'Start of ALARM0 registers
 #define MCP7940N_alarm1 0x11       'Start of ALARM1 registers
 #define MCP7940N_powerDown 0x18    'Start of power loss timestamp registers
 #define MCP7940N_powerUp 0x1C      'Start of power restoration timestamp registers

;Variables
 Dim Sec As byte
 Dim Sec2 As byte
 Dim Min As byte
 Dim Hour As byte
 Dim DayOfWeek as byte
 Dim CDate as byte
 Dim CMonth as byte
 Dim CYear as Byte
 Dim va as byte
 va=0
 Sec=0
 Min=0
 Hour=0
 CDate=0
 CMonth=0
 CYear=0

 'On first application of power to the device the time and date registers
 'are typically reset to 01/01/00 01 00:00:00 (MM/DD/YY DOW HH:MM:SS).
 'The CH bit in the seconds register will be set to a 0
 'Set Bit 7 of 00h register. Oscillator is enabled, clock start
 Sub MCP7940N_Enab_Osc

     I2CSTART
     I2CSEND ( MCP7940N_AddrWrite )
     I2CSEND ( 0 )
     I2CSTART
     I2CSEND ( MCP7940N_AddrRead )
     I2CReceive ( sec, NACK )
     Sec=BcdToDec( Sec )
     Sec=  Sec | 128
     I2CSTART
     I2CSEND ( MCP7940N_AddrWrite )
     I2CSEND ( 0 )
     I2CSEND ( DecToBcd(sec) )
     I2CStop

 end sub
</font>

Copy of my code below:

<font color="0000AA">
;Chip Settings
#chip 16F914,8
#config CP=OFF, MCLRE=ON, PWRTE=ON, WDT=OFF, OSC=INTRC_OSC_NOCLKOUT

;Include files (Libraries)
#include <mcp7940n.h>

;Defines (Constants)
#define LCD_IO 8
#define LCD_RW PORTD.6
#define LCD_RS PORTD.7
#define LCD_Enable PORTD.5
#define LCD_DATA_PORT PORTB
#define I2C_MODE Master
#define I2C_DISABLE_INTERRUPTS ON
#define I2C_DATA PORTC.7
#define I2C_CLOCK PORTC.6

;Variables
Dim hr As byte
Dim mn As byte
Dim sc As byte
Dim i As byte
Dim initOsc As byte
Dim readReg As byte

MCP7940N_Enab_Osc
initOsc = sec
Do Forever
    CLS
    DisplayTime
    Locate 1, 0
    Print initOsc
    Wait 100 ms
Loop
END

Sub DisplayTime
    MCP7940N_ReadTime hr, mn, sc
    readReg = sec
    Print hr
    Locate 0, 2
    Print ":"
    Locate 0, 3
    Print mn
    Locate 0, 6
    Print ":"
    Locate 0, 7
    Print sc
    Locate 1, 8
    Print readReg
    Exit Sub
End Sub
</font>

Last edit: Peter 2014-05-24

DS1307 to MCP7490N - Clock resets to +48s?

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DS1307 to MCP7490N - Clock resets to +48s?

DS1307 to MCP7490N - Clock resets to +48s?

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DS1307 to MCP7490N - Clock resets to +48s?