User`s manual

CYDAS UDR Library User’s Guide Analog Input Boards - PCYDAS 8

Determining the maximum sampling rate in DOS

If you have installed the DOS version of the CYDAS UDR Library, a utility program called MAXRATE is

installed in the UDR Library installation directory (C:\MCC by default).

MAXRATE tests your computer and

advise you of the maximum sustainable convert and transfer rate.

The maximum rate for your computer is reported for two conditions. The first is with all interrupts enabled,

the second is with the time of day interrupt disabled (TOD). The convert and transfer rate with TOD disabled

will usually be faster.

Time of Day interrupt and A/D conversions

Many TSR's and device drivers "hook" into the

TOD interrupt. Using the TOD clock tick guarantees that every

1/18th of a second the routine will be woken up and can check status or do whatever the routine is designed to

do. Unfortunately this can create considerable overhead in the

TOD interrupt service routine and will introduce

gaps in your sample data at high rates.

Using the

cbAInScan() / AInScan() option argument to turn off the TOD interrupt increases the speed that you

can maintain with your PCYDAS 8. Turning off the

TOD prevents your computer's clock from incrementing

while

cbAInScan() / AInScan() is running. Your clock will lose time.

Transfer rate

Any rate below 5 kHz is sustainable with or without TOD interrupt enabled. If your maximum required rate is

less than 5 kHz, then your computer can handle that. If the required rate is greater that 10K, run

MAXRATE.

Remember, we are discussing the

TOTAL rate, not the per channel rate. If you want 3 channels at 5 kHz, the

total rate is 15 kHz. Run

MAXRATE to see if your computer is up to the task.

Background operation

MAXRATE tests your computer using the cbAInScan() / AInScan() routine in the foreground. If you choose

background operation, it may not sustain the maximum rate returned by

MAXRATE. For the fastest performance,

use

cbAInScan() / AInScan() in the foreground, with the TOD interrupt disabled.