Very OLD Error in one-wire example in the library manager
Posted: 11 Nov 2013 21:36
Already a very OLD one, signalled lightyears (yes, I know that is a distance) ago I think:
The time needed between the CONVERT_T command and the READ_SCRATCHPAD command has to be at least 750 millisecs (can be shorter if using a D18B20 type with resolutions < 12 bits). In the above example it is 120 microseconds!!!!!
This means that the scratcpad will be read before the tempconversion finished, at least the first and probably also the second loop. Eventually the readings will be OK because the first temp conversion will be finished.
Come on guys, so many starting people (will) have problems with this!!!
Code: Select all
//--- Perform temperature reading
Ow_Reset(PORTE, 2); // Onewire reset signal
Ow_Write(PORTE, 2, 0xCC); // Issue command SKIP_ROM
Ow_Write(PORTE, 2, 0x44); // Issue command CONVERT_T
Delay_us(120);
Ow_Reset(PORTE, 2);
Ow_Write(PORTE, 2, 0xCC); // Issue command SKIP_ROM
Ow_Write(PORTE, 2, 0xBE); // Issue command READ_SCRATCHPADThis means that the scratcpad will be read before the tempconversion finished, at least the first and probably also the second loop. Eventually the readings will be OK because the first temp conversion will be finished.
Come on guys, so many starting people (will) have problems with this!!!