Buffer transfers – Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi User Manual

Page 91

8H. Turbo C

II. SOFTWARE GUIDES - 8. Driver488/DRV

II-76

Personal488 User’s Manual, Rev. 3.0

All the power of C may be used to manipulate, print, store, and analyze the data read from the
IEEE 488 bus. For example, the following statements print the average of ten readings from the 195:

int i;
float sum;
sum=0.0;
for (i=0; i; i++) {
ieeewt(“enter 16\n”);
ieeescnf(“%*4s%e”,&voltage);
sum=sum+voltage;
}
printf(“The average of 10 readings is %g\n”,sum/10.0);

Buffer Transfers

Instead of using an

IEEERD(_)

function to receive the data from a device, we can direct

Driver488/DRV to place the response directly into a data buffer of our choosing. For example, each
reading from the 195 consists of 17 bytes: a four-byte prefix and an eleven-byte reading followed by
the two-byte command terminator. So, we can collect 100 readings in a 1700-byte array. To do this,
we must first allocate the required space in an array:

char hundred[1700];

Now that we have allocated a place for the readings, we can direct Driver488/DRV to put readings
directly into

hundred

with the

ENTER #count BUFFER

command:

ieeeprtf(“ENTER 16 #1700 BUFFER %d:%d\n”,
segment(hundred),offset(hundred));

This command consists of the keyword

ENTER

, followed by the bus device address (

), a number sign

(

), the number of bytes to transfer (

1700

), and the keyword

BUFFER

, followed by the memory address

of the buffer. The buffer address is specified as

segment:offset

where

segment

and

offset

are

each 16-bit numbers and the colon (

) is required to separate them. The

segment

and

offset

values

we need are returned by the

segment

and

offset

functions, respectively.

Once the data has been received, we can print it out:

for (i=0; i<1700; i++) putchar(hundred[i]);

The program could process the previous set of data while collecting a new set into a different buffer.
To allow the program to continue, specify

continue

in the command:

ieeeprtf(“ENTER 16 #1700 BUFFER continue\n”,
segment(hundred),offset(hundred));

Once we have started the transfer, we can check the status:

ieeewt(“status\n”);
ieeerd(response);
printf(“%s\n”,response);

The status that is returned is typically:

CS21 1 L100 000 T0 C0 P1 OK

Notice

which states a transfer is in progress, and

which shows we are still a listener. If the bus

device is so fast that the transfer completes before the program can check status, the response is

showing that the transfer is no longer in progress. We can also

WAIT

for the transfer to complete and

check the status again:

ieeewt(“wait\n”);
ieeewt(“status\n”);
ieeerd(response);
printf(“%s\n”,response);

This time the status must be

as the

WAIT

command waits until the transfer has completed. Now that

we know the transfer is complete, we are ready to print out the received data as shown above.