ST6380 Datasheet, PDF (12/82 Pages) STMicroelectronics – 8-BIT MCUs WITH ON-SCREEN-DISPLAY FOR TV TUNING

ST6380, ST6381, ST6382, ST6383, ST6388, ST6389
MEMORY SPACES (Cont’d)
Data ROM Addressing. All the read-only data are
physically implemented in the ROM in which the
Program Space is also implemented. The ROM
therefore contains the program to be executed and
also the constants and the look-up tables needed
for the program. The locations of Data Space in
which the different constants and look-up tables
are addressed by the ST6 Core can be considered
as being a 64-byte window through which it is pos-
sible to access to the read-only data stored in the
ROM. This window is located from the 40h ad-
dress to the 7Fh address in the Data space and al-
lows 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 in-
structions or read-only data. Indeed, the window
can be moved by step of 64 bytes along the ROM
in writing the appropriate code in the Write-only
Data ROM Window register (DRWR, location
C9h). The effective address of the byte to be read
as a data in the ROM is obtained by the concate-
nation 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 can not address
window above the 16K byte range.
Data ROM Window Register (DRWR)
Address: C9h - Write only
Reset Value: XXh
7
0
DRWR DRWR DRWR DRWR DRWR DRWR DRWR DRWR
7
6
5
4
3
2
1
0
DRWR7-DRWR0. These are the Data Rom Win-
dow bits that correspond to the upper bits of data
ROM program space. This register is undefined af-
ter reset.
Caution: This register contains at least one write
only bit. Single bit instructions (SET, RES, INC
and DEC) should not be used.
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 in-
terrupts drivers, as the driver cannot save and
than restore its previous content. If it is impossible
to avoid the writing of this register in interrupts
drivers, an image 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 inter-
rupt occurs between the two instructions the
DRWR register is not affected.
Figure 7. 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 1 0 1 0 0 0}
DATA SPACE ADDRESS
01 0 1100 1
59h
ROM
ADDRESS:A19h ^{0 0 1 0 1 0 0 0 0 1 1 0 0 1}
VR01573B
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