ST6391 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'ST6391' PDF : 68 Pages View PDF
ST6391,92,93,95,97,99
MEMORY SPACES (Continued)
Figure 13. Program ROM Page Register
PRPR
Program ROM Page Register
(CAh, Write Only)
D7 D6 D5 D4 D3 D2 D1 D0
PRPR0
PRPR1
PRPR2
PRPR3
UNUSED
D7-D5. These bits are not used.
PRPR4-PRPR0. These are the program ROM
banking bits and the value loaded selects the cor-
responding page to be addressed in the lower part
of 4K program address space as specified in Table
3. This register is undefined on reset.
Note. The number of bits implemented depends
on the size of the ROM of the device. Only the
lower part of address space has been bank-
switched because interrupt vectors and common
subroutines should be available all the time. The
reason of this structure is due to the fact that it is
not possible to jump from a dynamic page to an-
other, unless jumping back to the static page,
changing contents of PRPR, and, than, jumping to
a different dynamic page.
Care is required when handling the PRPR as it is
write only. For this reason, it is not allowed to
change the PRPR contents while executing inter-
rupts drivers, as the driver cannot save and than
restore its previous content. Anyway, this opera-
tion may be necessary if the sum of common rou-
tines and interrupt drivers will take more than 2K
bytes; in this case could be necessary to divide the
interrupt driver in a (minor) part in the static page
(start and end), and in the second (major) part in
one dynamic page. If it is impossible to avoid the
writing of this register in interrupts drivers, an im-
age of this register must be saved in a RAM loca-
tion, and each time the program writes the PRPR it
writes also the image register. The image register
must be written first, so if an interrupt occurs be-
tween the two instructions the PRPR is not af-
fected.
Table 3. ST639x Program ROM Page Register
Coding
Memory
PRPR3 PRPR2 PRPR1 PRPR0 PC11 Page
Static
X
X
X
X
1 Page
(Page 1)
0
0
0
0
0 Page 0
Page 1
0
0
0
1
0 (Static
Page)
0
0
1
0
0 Page 2
0
0
1
1
0 Page 3
0
1
0
0
0 Page 4
0
1
0
1
0 Page 5
0
1
1
0
0 Page 6
0
1
1
1
0 Page 7
1
0
0
0
0 Page 8
1
0
0
1
0 Page 9
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