1.0 Functional Description
CX25870/871
1.3 Device Description
Flicker-Free Video Encoder with Ultrascale Technology
1.3.8 Autoconfiguration and Interface Bits
The default operation of the CX25870/871 is tied into its 44 autoconfiguration
modes. Autoconfiguring the device occurs when bits CONFIG[5:3] and
CONFIG[2:0] in register 0xB8 are programmed to any state from 000000 to
101111. At the conclusion of this serial write, default values are copied from the
CX25870/871’s internal ROM into the most important timing registers that have
the indices 0x38 and 0x76 to 0xB4, inclusive. All other registers are not changed
at the conclusion of an autoconfiguration mode.
After an autoconfiguration command, the CX25870/871 device remains in the
same interface it was in before the command execution. Depending on which
autoconfiguration mode# was initiated, the CX25870/871 will expect to receive
either a 320x200, 320x240, 640x400, 640x480, 720x400, 720x480, 720x576,
800x600, or 1024x768 active digital input frame and output a NTSC or a PAL
composite and/or S-video signal. See Table 2-5 of this data sheet for a description
of CONFIG[5:0] and Appendix C for more detail on each autoconfiguration
mode.
Using an autoconfiguration mode is the easiest method for bringing up the
most popular desktop, game/Direct X, DOS boot-up screen, and DVD resolutions
with the encoder as both the timing and clock master. This is true even if the
graphics controller cannot utilize the CX25870/871 in master mode but must use
pseudo-master mode. To turn the direction of the SYNCs around so they are
transmitted by the graphics controller and received by the CX25870/871 simply
requires reprogramming the encoder via several serial writes.
The Interface bits that need to be changed are SLAVER, EN_BLANKO,
EN_DOT, and EN_OUT. Since the abilities of graphics controllers vary greatly,
Tables 1-7 through 1-12 have been compiled below to explain the relationship
between the Interface bits and the actual interface itself. Even more permutations
of the following interfaces below are possible but Tables 1-7 to 1-12 capture the
six most popular architectures.
Table 1-7. Master Interface without a BLANK* Signal (Default Immediately after any Autoconfiguration Command)
SLAVER (Bit 5 of
0xBA) ORed with
Slave Pin
EN_BLANKO
(MSb of Register
0xC6)
EN_DOT (Bit 6
of Register
0xC6)
EN_OUT (LSb
of Register
0xC4)
Interfaced Used
MASTER (default)
0
1
0
1
BLANK* is an output from the
CX25870/871 or BLANK* µs NOT
included as part of the interface.
1-22
Conexant
100381B
CONEXANT [ CONEXANT SYSTEMS, INC ]
