Measurement Computing Data Acquisition Systems rev.10.4 - Manual (Page 121)

where mod is defined as the integer remainder of performing an integer divide of retCount by scanCount.
Detection of a buffer overrun condition is the responsibility of the application.
If using a linear buffer (DatmCycleOff) and the acquisition is expected to continue past the end of the
allocated buffer size, a new buffer must be allocated and configured using this function in a timely manner to
avoid loss of data (as would be the case in an alternating or “ping-pong” buffer approach).
Typical Transfer Buffer Settings
The following table shows a set of are typical transfer buffer settings; it assumes scan group size of 4 channels
and sample size of 2 bytes.
Desired Buffer buf scanCount transferMask
Application allocated linear buffer of 50,000
scans updated on every sample App pointer to memory
(size = 50,000 x 4 x 2
= 400,000 bytes) 50,000 DatmCycleOff +
DatmUpdateSingle +
DatmUserBuf
Application allocated linear buffer of 100,000
scans updated by block App pointer to memory
(size = 100,000 x 4 x 2
= 800,000 bytes) 100,000 DatmCycleOff +
DatmUpdateBlock +
DatmUserBuf
Application allocated circular buffer of 40,000
scans updated on every sample App pointer to memory
(size = 40000 x 4 x 2
= 320,000 bytes) 40,000 DatmCycleOn +
DatmUpdateSingle +
DatmUserBuf
Application allocated circular buffer of 200,000
scans updated by block App pointer to memory
(size = 200,000 x 4 x 2
= 1,600,000 bytes) 200,000 DatmCycleOn +
DatmUpdateBlock +
DatmUserBuf
Driver allocated circular buffer of 40,000 scans
updated on every sample NULL (Driver allocates
= 40,000 x 4 x 2
= 320,000 bytes) 40,000 DatmUpdateSingle +
DatmDriverBuf
Driver allocated circular buffer of 200,000 scans
updated by block NULL (Driver allocates
= 200,000 x 4 x 2
= 1,600,000 bytes) 200,000 DatmUpdateBlock +
DatmDriverBuf
Prototypes
C/C++
daqAdcTransferSetBuffer(DaqHandleT handle, PWORD buf, DWORD scanCount,
DWORD transferMask);
Visual BASIC
VBdaqAdcTransferSetBuffer&(ByVal handle&, buf%, ByVal scanCount&, ByVal
transferMask&)
Program References
DAQADCEXO1.CPP, DAQADCEX02.CPP, DAQADCEX03.CPP, DAQADCEX05.CPP,
DAQADCEX07.CPP, DBK04EX.CPP, DBK07EX.CPP, DBK08EX.CPP, DBK09EX.CPP,
DBK12_13EX.CPP, DBK15EX.CPP, DBK16EX.CPP, DBK17EX.CPP, DBK18EX.CPP,
DBK19EX.CPP, DBK42EX.CPP, DBK43EX.CPP, DBK44EX.CPP, DBK45EX.CPP,
DBK50EX.CPP, DBK51EX.CPP, DBK52EX.CPP, DBK53_54EX.CPP, DAQEX.FRM (VB)
Programmer’s Manual 908594 Daq API Command Reference 4.2-65