saa6703ah NXP Semiconductors, saa6703ah Datasheet - Page 66

• Manufacturer Part Number: saa6703ah
• Description: Xga Analog Input Flat Panel Controller.
• Manufacturer: NXP Semiconductors

Philips Semiconductors
It should be noted that the characters are not stored
byte-aligned in the internal RAM due to the programmable
font sizes (see Fig.21). Due to this, a bit-exact address is
internally needed that points to the first bit of a character
inside an 8-bit data word. This internal character base
address is calculated new, each time data is written to
either the OSDT_CC_HI or OSDT_CC_LO register and is
incremented by 8 bits on each write to OSDT_CDEF.
During each write the actual value of the OSDT_CMASK
register is used. So for an 8
be defined, simply set OSDT_CC to the desired charcode,
set all bits of OSDT_MASK to logic 1 and write 8 times to
OSDT_CDEF to define the complete character. For a 9
single colour character (needs 81 bits) you have to do
11 writes to OSDT_CDEF, even if only the MSB of the 11th
transmission is used and the remaining 7 bits stay unused.
One could now either use masked writing to mask those
bits 6 to 0 out (so the following character definition is not
touched) or immediately continue with the definition of the
next character and simply connect the next character data
to bit 6 down to bit 0. Because the IC cannot determine
which functionality is desired, the user can select this by
setting the OSDT_CC register. If an automatic masking at
the end of each character is desired, the flag
single_char_def (OSDT_CC_HI[7]) can be set to logic 1.
This means that before the next character definition the
2004 Apr 01
handbook, full pagewidth
XGA analog input flat panel controller
a. Single colour definition sequence
(needs 9
BYTE 4
11 = 99 bits
BYTE 3
OSDT_FR_X (= 9)
BYTE 2
BYTE 1
8 single colour character to
...
Fig.21 Data format of the OSD font RAM.
13 bytes).
9
66
desired charcode must be written again, because the
internal bit address does not longer match with the
following character base address. Otherwise, if this bit is
kept to logic 0, the internal bit address is continued over
character boundaries allowing multiple bit-packed
character transmission in a sequence. Only the last
definition might need a manual masked writing in case of
an address space overflow or if any needed data is present
at higher charcodes.
To reduce the programming time for the font RAM, an
auto-increment function is used internally so that an
I
many 8-bit data words as needed, even configuring all
characters in one continuous burst. To allow this, the
SAA6703AH register auto-increment is re-addressing
OSDT_CDEF after each write to OSDT_CDEF.
Any changes to the OSD text RAM definitions can also be
made while the OSD is displayed. So the usable character
set is only limited by the size of the external
microcontrollers ROM. Just keep in mind that due to
internal address calculation, the font size (OSDT_FR_X
and OSDT_FR_Y) and the single colour start code
(OSDT_SC_LO and OSDT_SC_HI) must be defined prior
to any font definition, in order that the character data will
not look disturbed.
2
C-bus burst transmission can be used to transmit as
(needs 9
b. Multicolour definition sequence
BYTE 3
BYTE 1
11
OSDT_FR_X (= 9)
2 = 198 bits
BYTE 4
BYTE 2
SAA6703AH
Product specification
...
MHC228
25 bytes).