Table of Contents
Advertisement
Address Window
With the lower address window, the FLC can access the first 512 (2 x 256) bytes of
the RAM physically without needing to load the base pointer. The advantage of this
is that the FLC can access the general parameters or the SAP list directly without
first needing to load the base pointer.
The entire internal memory can be addressed via the second address window of
256 bytes (200h to 2FFh) with the aid of an 8-bit base pointer. This pointer must be
loaded by the FLC and always addresses the beginning of an 8 byte segment (in
the extended SPC 4-2 mode, 16 bytes). This means that the FLC can address up
to 256 bytes using the offset address applied to the address pins of the SPC 4-2.
The third address window which is also 256 bytes long (300h to 3FFh) is used to
address the internal latches required for direct control of the hardware. These
latches are not integrated in the internal RAM area!
Address bit
A9
0
0
1
1
Table 4-2 Window Select
Notice:
Overwriting the address area is not prevented by the hardware; in other
words, if the user writes beyond the node table, the parameters are
overwritten in the lower memory area due to the "wraparound" function. In
this case, the SPC 4-2 generates the Mem-Overflow interrupt.
If read-only parameters are written to, an access violation interrupt is
generated.
PROFIBUS Controller SPC 4®-2 LF
C79000-G8976-C157-3
Address bit
A8
0
Parameter area (physically 00h-FFh)
1
Parameter area (physically 100h-1FFh)
0
Entire RAM using base pointer
1
Parameter register
Memory Assignment
Window Select
21
Advertisement
Table of Contents
