Measurement-computing TempBook rev.3.0 Manual do Utilizador descarregar pdf (Página 71)

TempBook User’s Manual tbkCommand Reference (

Standard

API) 9-11

tbkRdNBack

DLL Function

int tbkRdNBack(uint *buf, uint count, uchar cycle, uchar update Single);

tbkRdNBack(unsigned _far *buf, unsigned count, unsigned char cycle, unsigned

char updateSingle);

QuickBASIC

BtbkRdNBack% (buf%, ByVal count%, ByVal cycle%, ByVal updateSingle%)

Visual Basic

VBtbkRdNBack% (buf%(), count%, cycle%, updateSingle%)

Turbo Pascal

tbkRdNBack( buf:WordP; count:word; cycle:byte; updateSingle:byte ):integer;

Parameters

uint *buf

An array where the A/D scans will be placed

uint count

The number of scans to be taken

Valid values: 1 - 32767

uchar cycle

A flag that if non-zero will enable continuous operation, or if 0 will disable it

uchar updateSingle

A flag that if non-zero will enable single scans to be read into buf or if 0 will enable buf to be updated in

a block of 256 scans

Returns

TerrMultBackXfer

- Background read already in progress

TerrNoError

- No error

See Also

tbkGetBackStat, tbkBackStop, tbkSetTag, tbkSetClk, tbkSetTrig

Program References

None

tbkRdNBack

reads multiple A/D scans in the background using interrupts. This function will

return control back to the user’s program after initiating the background transfer. The user can then

monitor the status of the background transfer with the

tbkGetBackStat

function or stop the

transfer with the

tbkBackStop

function. Because the transfer occurs in the background, the user

can perform other tasks in the foreground. This function assumes that the A/D acquisition has

already been setup.

If the cycle flag is true, the background transfer will run continuously looping back to the beginning

of ‘buf’ after ‘count’ scans have been read. This allows the user to read large amounts of data

without calling

tbkRdNBack

multiple times. As long as the user monitors how much data is in the

buffer and processes the data before it gets overwritten, the background transfer can run indefinitely.

In this mode, the user should get the total number of scans written into ‘buf’ using

tbkGetBackStat

and keep track of the total number of scans processed in a variable. The

difference between these two totals is the number of unprocessed valid scans in ‘buf’ that the user

can process.

Note: the Visual Basic chapter includes an example program which demonstrates how to use the

cycle mode of

tbkRdNBack

The

updateSingle

flag allows the user to control whether the TempBook/66 updates ‘buf’ one

sample at a time or in blocks of 256 scans. Enabling

updateSingle

allows the user to read A/D

data during slow acquisitions as the data is acquired. Because the

updateSingle

flag is directly

tied to the number of interrupts that will be generated on the computer, the flag should not be

enabled if the acquisition rate is greater than roughly 500 scans per second (sampling rate * # of

channels). For example, an acquisition running at 1 Hz might enable the

updateSingle

flag so

that the data can be read each second rather than waiting for 256 seconds. An acquisition running at

10,000 Hz would disable the flag so the computer does not hang.

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