ST6391 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'ST6391' PDF : 68 Pages View PDF
ST6391,92,93,95,97,99
MEMORY SPACES
The MCUs operate in three different memory
spaces: Stack Space, Program Space, and Data
Space. A description of these spaces is shown in
Figure 11.
Stack Space
The stack space consists of six 12 bit registers that
are used for stacking subroutine and interrupt return
addressesplus the current programcounterregister.
Program Space
The program space is physically implemented in
the ROM and includes all the instructions that are
to be executed, as well as the data required for the
immediate addressing mode instructions, the re-
served test area and user vectors. It is addressed
thanks to the 12-bit Program Counter register (PC
register) and so, the ST639x Core can directly ad-
dress up to 4K bytes of Program Space. Neverthe-
less, the Program Space can be extended by the
addition of 2-Kbyte ROM banks as it is shown in
Figure 13 in which a 20K bytes memory is de-
scribed. These banks are addressed by pointing to
the 000h-7FFh locations of the Program Space
thanks to the Program Counter, and by writing the
appropriate code in the Program ROM Page Reg-
ister (PRPR) located at the CAh address of the
Data Space. Because interrupts and common sub-
routines should be available all the time only the
lower 2K byte of the 4K program space are bank
switched while the upper 2K byte can be seen as
static space. Table 3 gives the different codes that
allows the selection of the corresponding banks.
Note that, from the memory point of view, the Page
1 and the Static Page represent the same physical
memory: it is only a different way of addressing the
same location. On the ST6392,95,97, a total of
2048, bytes of ROM have been implemented;
20140 are available as user ROM while 340 are re-
served for testing.
Figure 12. ST639x 20K Bytes Program Space
Addressing Description
Program
counter
space
0000h
0FFFh
Static Page
Page 1
0800h
07FFh
Page 0
Page 1
Static Page
0000h
4FFFh
Page 9
Figure 11. ST639x Memory Addressing Description Diagram
STACK SPACE
PROGRAM SPACE
DATA SPACE
PROGRAM COUNTER
STACK LEVE L 1
STACK LEVE L 2
STACK LEVE L 3
STACK LEVE L 4
STACK LEVE L 5
STACK LEVE L 6
00 00h
ROM
07FFh
08 00h
ROM
0FF0h
0 FFF h
IN TER RU PT &
RESET VECTORS
0-63
00 0 h
R AM / E EPROM
B AN KING AR EA
03 F h
04 0 h
07 0 h
08 0 h
08 1 h
08 2 h
08 3 h
08 4 h
0C0 h
D ATA R OM
WINDOW
X RE GISTER
Y R EGISTER
V RE GISTER
W REGISTER
R AM
D ATA R OM
WI N D OW SELEC T
D ATA R AM
BANK SELEC T
0FFh ACCUMULATOR
VR001568
10/64
®
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