TMAutoOverDrive Overview Group

The TMAutoOverDrive API call sets TMEX to automatically switch to Overdrive communication speed if the 1-Wire device, 1-Wire network and driver support it. This is done by doing all serial ROM searches at normal 1-Wire speeds and switching to Overdrive speeds when the device is accessed with TMAccess. Automatic Overdrive is selected if the ‘Mode’ is 1 and not selected if ‘Mode’ is 0. Under the following conditions the TMEX driver will switch to Overdrive:

  1. TMAutoOverDrive has be called with Mode = 1

  2. The serial ROM number family type supports Overdrive

  3. TMAccess is called.  Note that TMAccess is automatically called in high level memory functions.

  4. Successful communication to the part is achieved at Overdrive speeds

The following conditions will switch the TMEX driver out of Overdrive if communication is currently in Overdrive due to TMAutoOverDrive:

  1. Any search NETWORK API call such as TMFirst or TMNext. A change to the serial ROM number using TMRom.

  2. A failure of TMAccess at Overdrive speeds

  3. End to the Session on that 1-Wire network.

short far pascal TMAutoOverDrive(
long session_handle,         // session handle for the desired 1-Wire network
void far *state_buffer,      // state buffer provided for the 1-Wire network session
short Mode                   // Auto Overdrive mode selection

For a description of the above types, see the TMEX Type Descriptions.



Specifies the session handle returned from the API function TMExtendedStartSession that specifies the desired 1-Wire network port. This parameter is required by most TMEX API functions.


Specifies a pointer to a memory location that TMEX keeps all of the state information for the 1-Wire networks. This parameter is required by most TMEX API functions.


Specifies Auto-Overdrive mode that is to be selected. A Mode of 1 will indicate that Overdrive speed should be attempted whenever possible. A Mode of 0 will indicate that only normal communication speed should be used.

Return Value

1 => Auto-overdrive mode set

<0 => TMEX Network Error Return Code

Code Example

See Also

TMOverAccess, TMOneWireCom