HP E1340A, User Manual

Page: 233 / 295

The Register Offset
and Register Number
Depending on whether absolute addressing or select code 8 is used, either a
register offset or register number is specified as part of the register address.
Absolute addressing specifies a register offset, which is the register’s
location in the block of 64 address bytes. For example, the AFG’s
Command Register has an offset of 08
16
. When you write a command to
this register, the offset is added to the base address to form the register
address (using a logical address of 80):
register address = base a register offset
= 1FC000
16
+ (80 * 64)
16
+ 08
16
= 1FC000
16
+ 1400
16
+ 08
16
= 1FD408
16
or
= 2,080,768 + (80 * 64) + 8
= 2,080,768 + 5120 + 8 = 2,085,896
Using select code 8 requires that you specify a register number. The
register number is the register offset/2. Referring to Figure C-1A, the
Command Register with an offset of 08, is register number 4.
Note
The example programs found in this appendix are IBASIC programs using
absolute addressing.
External Computer
Programming
When the AFG is programmed by an external computer through the
E1300/E1301 mainframe or E1405/E1406 Command Module, the registers
are accessed using
DIAG:PEEK?
and
DIAG:POKE
, or
VXI:READ?
and
VXI:WRITE
.
DIAG:PEEK?/DIAG:POKE and VXI:READ?/VXI:WRITE
Throughput speed using DIAG:PEEK? and DIAG:POKE is faster than
VXI:READ? and VXI:WRITE because the complete register address
(including the A16 starting location 1FC000
16
) is specified. VXI:READ?
and
VXI:WRITE
specify the device logical address and register offset only.
Thus, the E1300/01/E1405/06 processor must calculate the complete
register address which decreases throughput speed.
IBASIC programming using absolute addressing or select code 8 is faster
than either
DIAG:PEEK?
and
DIAG:POKE
or
VXI:READ?
and
VXI:WRITE
because the registers are accessed from the VXIbus backplane rather than
from the HP-IB. Also,
READIO
and
WRITEIO
are not parsed.
Appendix C HP E1340A Register-Based Programming 233