Measurement Computing Personal488 rev.3.0 For DOS & Windows 3.Xi - Manual (Page 72)

II. SOFTWARE GUIDES - 8. Driver488/DRV 8E. Microsoft C
Personal488 User’s Manual, Rev. 3.0 II-57
Configuration of the 195 DMM
Once the system is initialized we are ready to start issuing bus commands. The IEEE 488 bus has
already been cleared by the Interface Clear (
IFC ) sent by the RESET command, so we know that all bus
devices are waiting for the controller to take some action. To control an IEEE 488 bus device, we
output an appropriate device-dependent command to that device. For example, the
F0R0X command
line below sets the 195 to read DC volts with automatic range selection:
ieeewt(“output 16;F0R0X\n”);
The OUTPUT command takes a bus device address ( 16 in this case) and data ( F0R0X ) and sends the data
to the specified device. The address can be just a primary address, such as 12 , or 05 , or it can include
a secondary address: 1201 . Note that both the primary address and, if present, the secondary address
are two-digit decimal numbers. A leading zero must be used, if necessary to make a two-digit address.
Taking Readings
Once we have set the 195’s operating mode, we can take a reading and display it:
float voltage;
ieeewt(“enter 16\n”);
ieeescnf(“%*4s%e”,&voltage);
printf(“The read value is %g\n”,voltage);
The ENTER command takes a bus address (with an optional secondary address) and configures that bus
device so that it is able to send data (addressed to talk). No data is actually transferred, however, until
the
IEEESCNF statement requests the result from Driver488/DRV at which time data is transferred to
the program into the variable voltage . A typical reading from a 195 might be NDCV+1.23456E-2 ,
consisting of a four character prefix followed by a floating point value. The format passed to
IEEESCNF causes it to skip the four character prefix ( %*4s ) and then convert the remaining string into
the float variable voltage .
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:
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 ( 16 ), 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
int i;
float sum;
sum=0.0;
for (i=0; i<10; i++) {
ieeewt(“enter 16\n”);
ieeescnf(“%*4s%e”,&voltage);
sum=sum+voltage;
}
printf(“The average of 10 readings is %g\n”,sum/10.0);