83C055 Philips Semiconductors, 83C055 Datasheet - Page 19

• Manufacturer Part Number: 83C055
• Description: Microcontrollers for TV and video MTV
• Manufacturer: Philips Semiconductors

Philips Semiconductors
13.6
The programming interface to Display RAM is provided by
three Special Function Registers as shown in Tables 15,
17 and 20.
Writing OSAT simply latches the attribute bits into a
register, while writing OSDT causes the data bus
information, plus the contents of the OSAT register, to be
written into display RAM.
Thus, for a given Display RAM location, OSAT should be
written before OSDT. If successive characters are to be
written into Display RAM with the same attributes, OSAT
13.6.1
Table 15 Special Function Register OSAD (On Screen ADdress; address 9AH)
Table 16 Description of OSAD bits
13.6.2
Writing OSDT causes the data bus information, plus the contents of the OSAT register, to be written into display RAM.
Table 17 Special Function Register OSDT (On Screen DaTa; address 99H)
Table 18 Description of OSDT bits
1996 Mar 22
Microcontrollers for TV and video (MTV)
6 to 0
7 to 6
5 to 0
BIT
BIT
7
7
7
OSD Special Function Registers
S
S
PECIAL
PECIAL
F
F
OSAD6
UNCTION
UNCTION
OSAD6 to OSAD0
OSDT5 to OSDT0
6
6
SYMBOL
SYMBOL
R
R
EGISTER
EGISTER
OSAD5
OSDT5
5
5
OSAD
OSDT
Reserved.
These 7-bits hold the Display RAM address into which data will be
loaded. OSAD is automatically incremented by one each time OSDT and
Display RAM are written to.
Reserved.
Character data; see Table 19. In reality, there is a potential conflict
between the timing of a write to OSDT and an access to display RAM by
the OSD logic for data display. This is resolved by the use of a true
dual-ported RAM for display memory.
OSAD4
OSDT4
4
4
19
need not be rewritten for each character, only prior to
writing OSDT for the first character with those particular
attributes.
The OSAT attribute bits associated with the BSpace,
SplitBSpace and New Line characters (see Table 19) are
interpreted differently from those that accompany other
data characters. With BSpace and SplitBSpace, B is
interpreted as described above, but the 3 colour bits
specify the background colour (Bcolor) for subsequent
characters. For BSpace, a change in B and Bcolor
becomes effective at the left edge of the character’s bit
map.
OSAD3
OSDT3
3
3
DESCRIPTION
DESCRIPTION
OSAD2
OSDT2
2
2
83C145; 83C845
83C055; 87C055
OSAD1
OSDT1
1
1
Product specification
OSAD0
OSDT0
0
0