TMC2081 Datasheet, PDF (7/32 Pages) Fairchild Semiconductor – Digital Video Mixer

PRODUCT SPECIFICATION
TMC2081
M23-0 bits are clocked synchronously with the rising edge of
CLK. M23-0 data outputs may be disabled to a high-imped-
ance state by setting the MOUT Control Register bit LOW.
Analog Preview
Either crosspoint switch input (A or B) or the mixed
pixel data output (M23-0 ) can be monitored by D/A
con-verters. D/A outputs may be either YCBCR or GBR.
A YCBCR-to-GBR matrix prior to the D/A converters can
be selected for color-space conversion.
To view A or B data originating in the CBCR format, the
DACFRM Control Register bit must be set to convert 2’s-
complement data to the offset binary format.
With the DACSLP bit, D/A converters can be powered down
and with the DACOVL bit, the D/A overlay RAM can be
powered down.
D/A Converter Outputs
Each D/A converter comprises an array of current sources
referenced to VDD and controlled by the data, BLANK, and
SYNC inputs. When BLANK = HIGH, the SETUP Control
Register bit determines if a pedestal is activated. With nomi-
nal RREF and VREF, outputs match SMPTE 170M levels
when terminated with a 37.5W resistive load (75W at the
source and destination). By doubling RREF, a 75W load can
be accommodated.
Full scale current is set by an external resistor, RSET, con-
nected between the RREF pin and AGND and the reference
voltage, VREF. VREF may be derived from either a 1.235 volt
internal source or an external voltage reference connected to
VREF.
Nominal outputs (see Figure 2 and Figure 3) are expressed in
Current Units (IU) where 1 IU is equivalent to the current
activated by one unit of D/A input data (Gdata/Ydata, Bdata/
CRdata, or Rdata/CBdata). SETUP = HIGH activates a 21 IU
pedestal when BLANK= H. SYNC = LOW disables a 110
IU sync pulse. SETUP is programmed through Register 7
bit 2.
data: 255 IU max.
pedestal: 21 IU
sync: 110 IU
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Figure 2. GBR/Y DAC Output Levels in Current Units
128
max.: 255 IU
0
blank: 128 IU
-127
min.: 0 IU
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Figure 3. CBCR DAC Output Levels in Current Units
To translate IUs to millivolts, VREF and RSET must be set
to the correct values, nominally VREF = 1.235 volt and
RSET = 681 ohms. In each table below, G and the Y outputs
have been normalized to 1000 mV with Data = 255.
Since VREF and RREF are common to all D/A converters,
B and R full scale outputs track G. C_B C_R full scale outputs
track Y. RREF may be trimmed to set the G or Y full scale
voltage to 1000 mV.
In the equations for the GBR and YCBCR outputs that follow,
symbols are defined as:
+ = plus
* = multiply
& = logical AND
! = logical complement
GBR Output
Expressed in IUs, the GBR transformation from data to
current is as follows:
G = (Gdata + SETUP * 21) & BLANK + SYNC * 110
B = (Bdata + SETUP * 21) & BLANK
R = (Rdata + SETUP * 21) & BLANK
Sample outputs are listed in Table 9 and Table 10.
Table 9. GBR DAC Transfer Characteristic
without Pedestal (SETUP = L)
D/A
Input
Data SYNC BLANK
G
IU mV
B or R
IU mV
255 1
1
365 1000 255 699
128 1
1
238 652 128 351
0
1
1
110 301 0
0
X
1
0
110 301 0
0
X
0
0
0
0
0
0
128 0
1
128 351 128 351
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