参数资料
型号: ST72774S9T1/XXX
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PQFP44
封装: TQFP-44
文件页数: 144/144页
文件大小: 1280K
代理商: ST72774S9T1/XXX
ST72774/ST727754/ST72734
99/144
DDC INTERFACE (Cont’d)
4.8.5 DDC Standard
The DDC standard is divided in several data
transfer protocols: DDC1, DDC2B, DDC/CI.
For DDC1/2B, refer to the “VESA DDC Standard
v3.0” specification. For DDC/CI refer to the “VESA
DDC Commands Interface v1.0”
– DDC1 is a uni-directional transmission of EDID
v1 (128 bytes) from display to host clocked by
VSYNCI.
– DDC2B is a uni-directional channel from display
to host. The host computer uses base-level I2C
commands to read the EDID data from the dis-
play which is always in slave mode.
Specific types of display contain EDID at fixed
I2C device addresses within the device (refer to
Table 25).
– DDC/CI is a bi-directional channel between the
host computer and the display. The DDC/CI of-
fers a display control interface based on I2C bus.
It includes the DDC2Bi and DDC2AB standards.
Note: The DDC2AB standard is no longer handled by the
interface.
4.8.5.1 DDC1/2B Interface
4.8.5.1.1 Functionnal description
Refer to the DCR, AHR registers in Section 4.8.6.
for the bit definitions.
The DDC1/2B Interface acts as an I/O interface
between a DDC bus and the microcontroller
memory. In addition to receiving and transmitting
serial data, this interface directly transfers parallel
data to and from memory using a DMA engine,
only halting CPU activity for two clock cycles
during each byte transfer.
The interface supports by hardware:
– Two DDC communication protocols called DDC1
and DDC2B.
– Write operations into RAM.
– Read operations from RAM.
In DDC1, the interface reads sequential EDID v1
data bytes from the microcontroller memory, and
transmits them on SDA synchronized with Vsync.
In DDC2B mode, it operates in I2C slave mode.
The DDC1/2B Interface supports several DDC
versions configured using the CF[2:0] bits in the
DCR register which can only be changed while the
interface is disabled (HWPE bit=0 in the DCR
register). They define which EDID structure
version is used and which Device Addresses are
recognized.
Depending on the DDC version, one or two device
address
pairs
will
be
recognized
and
the
corresponding EDID structure will be validated
(refer to Table 25):
– DDC v2 (CF2=0,CF1=0,CF0=0): DDC1 is ena-
bled and device addresses A0h/A1h are recog-
nized. EDID v1 is used.
– DDC v2 (CF2=1,CF1=0,CF0=0): DDC1 is disa-
bled and device addresses A0h/A1h are recog-
nized. EDID v1 is used.
– Plug and Display (CF2=0,CF1=0,CF0=1):
DDC1 is disabled and device addresses A2h/
A3h are recognized. EDID v2 is used.
– Plug and Display + DDC v2 (CF2=0,CF1=1,
CF0=0): DDC1 is enabled and device addresses
A0h/A1h and A2h/A3h are recognized. Both
EDID structures v1 and v2 are used.
– Plug and Display + DDC v2 (CF2=1,CF1=1,
CF0=0): DDC1 is disabled and device addresses
A0h/A1h and A2h/A3h are recognized. Both
EDID structures v1 and v2 are used.
– FPDI (CF2=0,CF1=1, CF0=1): DDC1 is disabled
and device addresses A6h/A7h are recognized.
EDID v2 is used.
Table 25. Valid Device Addresses and EDID structure
Device Address
CF2 bit
CF1 bit
CF0 bit
Transfer Type
EDID v1:
A0h / A1h = 1010 000x
x
0
128-byte EDID structure write/read
EDID v2:
A2h / A3h = 1010 001x
001
256-byte EDID structure write/read
010
110
EDID v2:
A6h / A7h = 1010 011x
1
256-byte EDID structure write/read
reserved
1
x
1
reserved
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