corman44 / temp-monitor

temp-monitor

Debugging tools: gdb and openocd

DS18B20 Info https://datasheets.maximintegrated.com/en/ds/DS18B20.pdf

64-bit ROM Code [ 8-bit CRC | 48-bit Serial Number | 8-bit family code (28h) ]
^MSB LSB^ ^MSB LSB^ ^MSB LSB^

Memory Map

Byte 0: Temp LSB (50h)
Byte 1: Temp MSB (05h) (combo for 85degC)
Byte 2: T_H Reg or User Byte1 <-> Read from EEPROM
Byte 3: T_L Reg or User Byte2 <-> Read from EEPROM
Byte 4: Config Reg <-> Read from EEPROM
Byte 5: Reserved
Byte 6: Reserved
Byte 7: Reserved
Byte 8: CRC

Config Register

Bit7: 0, Bit6: R1, Bit5: R2, Bit4: 1, Bit3: 1, Bit2: 1, Bit1: 1, Bit0: 1
setting R1=R2=1 will enable 12 resolution bits at 750ms

CRC Generator

CRC = X^8 + X^5 + X^4 + 1

1-Wire Comm

DS18B20 is always in Slave mode. All data transmitted with LSB first
Transaction Sequence: Init, ROM Command, DS18B20 Function Command
Init: Master Tx Reset Pulse of > 480us, then release.

ROM Commands:

• Search ROM [0xF0]: during init process, Master needs to identify each slave
• Read ROM [0x33]: used when 1 device is connected. Allows Master to read the 64-bit ROM code. (not to be used with multiple slaves on bus)
• Match ROM [0x55]: this command followed by a 64-bit ROM Code sequence allows the master to address a specific slave device on a multi/singledrop bus. Only the slave with the matching address will respond. (until another reset pulse is sent)
• Skip ROM [0xCC]: allows master to send a command to all slaves
• Alarm Search [0xEC]: allows Master to determine if any device has reached the alarm stage. Init sequence must be followed for further commands.

DS18B20 Commands:

• Convert T [0x44]: this command initiates a single temp conversion. Bus is pulled low by slave for duration of t_CONV.
• Write Scratchpad [0x4E]: this command allows the master to write 3 bytes of data to the scratchpad. T_H, T_L, Config reg is the order (Byte2, Byte3, Byte4). Data transmitted LSB first before Master issues a reset.
• Read Scratchpad [0xBE]: allows the master to read the contents of the scratchpad. Transfer starts with LSB of Byte0 and continues through Byte8's MSB. Master may terminate the transmission part way through if not all Bytes are necessary.
• Copy Scratchpad [0x48]: commands the device to copy the data Bytes 2,3,4 to EEPROM for later usage.
• Recall E^2 [0xB8]: recalls alarm trigger values from EEPROM and places them in active data byte's 2,3,4. This command happens automatically at startup and slave will transmit 0 while the recall is in progress and 1 when it's done.
• Read Power Supply [0xB4]: followed by a read time slot to determine if any slaves on the bus are using parasite power mode. Internal powered slaves will pull the bus low and externally powered devices will let the bus remain high.

Read Time Slots:

• 1 is transmitted by leaving bus high and 0 is transmitted by pulling the bus low (V_PU or GND)
• Master Tx Reset Pulse 480us Minimum. Master Rx Mimimum of 480us
• Master writes '0' by pulling comm line low for 60us < Tx '0' < 120us then releases the line to pullup high

Example Sequence:

master mode	data (LSB First)	comment
Tx	Reset	master issues reset pulse
Rx	Presence	slave responds with presence pulse
Tx	0xCC	master issues Skip ROM Command
Tx	0x4E	master issues Write Scratchpad commmand
Tx	3 data bytes	master send T_H T_L and config bytes
Tx	Reset	master issues reset pulse
Rx	Presence	slave responds with presence pulse
Tx	0xCC	master issues skip ROM command
Tx	0xBE	master issues Read Scratchpad command
Rx	9 data bytes	master reads and calculates CRC, sends command again if failed, otherwise continues
Tx	Reset	master issues reset command
Rx	Presence	slave responds with presence
Tx	0xCC	master issues Skip ROM command
Tx	0x48	master issues Copy Scratchpad command
Tx	DQ held high by pullup	master applies strong pullup to DQ for >10ms while copy operation is in progress