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)
Data ROM Addressing. All the read-only data are
physically implemented in the ROM in which the Pro-
gram Space is also implemented. The ROM therefore
containsthe programto be executedandalso the con-
stants and the look-up tables neededfor the program.
The locationsof Data Space in which the differentcon-
stants and look-up tables are addressed by the
ST639x Core can be considered as being a 64-byte
window through which it is possible to access to the
read-only data stored in the ROM. This window is lo-
cated from the 40h address to the 7Fh address in the
Data space and allows the direct reading of the bytes
from the 000h address to the 03Fh address in the
ROM. All the bytes of the ROM can be used to store
either instructions or read-only data. Indeed,the win-
dow can bemoved by step of 64 bytes alongthe ROM
in writing the appropriate code in the Write-only Data
ROM Window register (DRWR, location C9h). The ef-
fective address of the byte to be read as a data in the
ROM is obtained by the concatenation of the 6 less
significant bits of the address in the Data Space (as
less significant bits) and the content of the DRWR (as
most significant bits). So when addressing location
40h of data space, and 0 is loaded in the DRWR, the
physical addressed location in ROM is 00h.
Note. The data ROM window cannot address win-
dows above the 16k byte range.
Figure 16. Data ROM Window Register
DWR
Data ROM Window Register
(C9h, Write Only)
D7 D6 D5 D4 D3 D2 D1 D0
DWR0 = Data ROM Window 0
DWR1 = Data ROM Window 1
DWR2 = Data ROM Window 2
DWR3 = Data ROM Window 3
DWR4 = Data ROM Window 4
DWR5 = Data ROM Window 5
DWR6 = Data ROM Window 6
DWR7 = Data ROM Window 7
DWR7-DWR0. These are the Data Rom Window
bits that correspond to the upper bits of data ROM
program space. This register is undefined after re-
set.
Note. Care is required when handling the DRWR as
it is write only. For this reason, it is not allowed to
change the DRWR contents while executing inter-
rupts drivers, as the driver cannot save and than re-
store its previous content. 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 location,
and each time the program writes the DRWR it
writes also the image register. The image register
must be written first, so if an interrupt occurs be-
tween the two instructions the DRWR register is not
affected.
Figure 17. Data ROM Window Memory Addressing
DATA ROM
13 12 11 10 9 8 7 6 5 4 3 2 1 0 PROGRAM SPACE ADDRESS
WINDOW REGISTER 7 6 5 4 3 2 1 0
READ
CONTENTS
(DWR)
5 4 3 2 1 0 DATA SPACE ADDRESS
01
40h-7Fh
IN INSTRUCTION
Example:
DWR=28h 0 0
10
10
00
0 10
110 0
DATA SPACE ADDRESS
1
59h
ROM
ADDRESS:A19h 0 0 1 0 1 0 0 0 0 1 1 0 0 1
VR01573B
14/64
®
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