LM1236 National Semiconductor Corporation, LM1236 Datasheet - Page 34

• Manufacturer Part Number: LM1236
• Description: 150 Mhz I2c Compatible Rgb Preamplifier With Internal 254 Character Osd Rom, 512 Character Ram And 4 Dacs
• Manufacturer: National Semiconductor Corporation

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Control Register Definitions
ROM Signature Control Register:
ROM Signature Data:
Display Window 1 Horizontal Start Address:
Display Window 1 Vertical Start Address:
Display Window 1 Start Address:
X
X
Bits 8–0
Bits 15–9
Bit 0
Bits 7–1
Bits 15–0
Bits 7–0
Bits 7–0
X
X
ROMSIGDATAB1 (0x840F)
CHSDWCTRLB1 (0x840A)
X
X
W1STRTADRH (0x8413)
Reserved
Reserved
These registers determine the heavy button box lowlight, shading or shadow color.
Reserved. These bits should be set to zero.
This controls the calculation of the ROM signature. Setting this bit causes the ROM to be read
sequentially and a 16-bit checksum calculated over the 254 characters. The sum, modulo 65535, is
stored in the ROM Signature Data Register, and this bit is then automatically cleared.
Reserved. These should be set to zero.
This is the checksum of the 254 ROM characters truncated to 16 bits (modulo 65535). All devices
with the same masked ROM will have the same checksum.
There are two possible OSD windows which can be displayed simultaneously or individually. This
register determines the horizontal start position of Window 1 in OSD pixels (not video signal
pixels). The actual position, to the right of the horizontal flyback pulse, is determined by multiplying
this register value by 4 and adding 30. Due to pipeline delays, the first usable start location is
approximately 42 OSD pixels following the horizontal flyback time. For this reason, we recommend
this register be programmed with a number larger than 2, otherwise improper operation may result.
This register determines the Vertical start position of the Window 1 in constant-height character
lines (not video scan lines). The actual position is determined by multiplying this register value by
2. (Note: each character line is treated as a single auto-height character pixel line, so multiple scan
lines may actually be displayed in order to maintain accurate position relative to the OSD character
cell size. See the Constant Character Height Mechanism section.) This register should be set so
the entire OSD window is within the active video.
X
X
X
X
X
X
X
X
Window 1 Horizontal Start Location
Window 1 Vertical Start Address
X
(Continued)
X
X
ROMSIGCTRL (0x840D)
Reserved
HSTRT1 (0x8410)
16-Bit Checksum
VSTRT1 (0x8411)
X
CRC[15:0]
Shadow - Green
1H[7:0]
1V[7:0]
34
G[2:0]
X
X
Window 1 Start Address
ROMSIGDATAB0 (0x840E)
CHSDWCTRLB0 (0x8409)
W1STRTADRL (0x8412)
Shadow - Red
X
1AD[8:0]
R[2:0]
check
CRS
Shadow - Blue
B[2:0]