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參數(shù)資料
| 型號： | TPU2735 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Teletext Processor |
| 中文描述： | 圖文處理器 |
| 文件頁數(shù)： | 30/37頁 |
| 文件大小： | 1019K |
| 代理商： | TPU2735 |
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TPU 2735
30
11. Application Notes
Problem:
Clamping of External RGB Signals
The external RGB inputs are fed through the TPU to the
VCU. Clamping of these signals is done by the VCU dur-
ing the color key pulse. The RGB switches of the TPU
are controlled by the external “Fast Blank” input to the
TPU and by internal control bits (TTM, RGBE, please re-
fer to sections 3.3., 6.4.). In some cases the external fast
blank signal is switched off during the horizontal blank-
ing interval (e.g. PIP insertion and OSD active). In these
cases the external RGB inputs are not switched to the
VCU during the blanking interval and the clamping fails.
To force clamping of the RGB inputs in all modes the col-
or key should be ‘ored’ to the external fast blank signal.
Problem:
Conflict flag
The conflict flag in the page request register is set if the
TPU273x has opened a page for acquisition and re-
ceives a header row for another page that is requested
in some other request register. This usually happens
when the last page of a magazine is requested. In the
case of a conflict the internal logic of the TPU assigns the
highest priority to the page selected for display. Setting
the ‘no updating’ flag for this page will resolve the con-
flict. (In order to get an ‘open’ page into NUF mode one
should set NUP and NRF.) Also the behavior of the ac-
quisition circuit is influenced by the open (OPN) bit in the
page selection register. This bit forces the acquisition
circuit to keep pages open and thereby makes conflict
situations worse. This bit should be zero for normal Tele-
text acquisition.
Continuous long updating times for the ‘time’ field are
also influenced by the conflict.
The World System Teletext Specification reserves a
Row0 of page 0xFF (hexadecimal) for the function of
magazine close row. Transmitting this row would solve
all of these problems.
Problem:
Spanish Teletext
As the decoding of the information transmitted in rows
26 is done by the CCU obviously the control program
has to check for the reception of any row26. The actual
row26 processing is only required for the page currently
displayed. This should be done in the ‘idle loop’ of the
control program. There is no other way than polling to
see if a row26 was received.
The ‘Spanish Teletext Specification’ requires the extra
characters to be transmitted with even parity. Therefore
a true ‘Spanish Teletext Page’ cannot be received with-
out errors and will be acquired again and again. (It is not
recommended to use the NPC mode.) A way to detect
the reception of a ‘new’ (i.e. different) page is to check
the subcode information stored in register chain one.
Usually a subcode of all zeros or all ones indicates a
non-rolling page.
Problem:
Initialization
Initialization of the TPU should always start with a clear
of register chain 2 via the CR2 bit in the R_MC register.
If the mode is switched to NTSC/D2MAC, setting the ap-
propriate control bit in register R_DC4 should be the
next action. Since internal clocks of the TPU are
switched by these bits, the next thing should be a clear
of all registers in register chain 2 (except the mode regis-
ter R_DC4). In case of NTSC mode, it is recommended
to set the NTSC bit, wait for two fields, check that the
NTSC bit is still set, and then start the clearing of register
chain 2. After this procedure the normal initialization of
registers should follow.
Samples for TPU2735-E are available and are marked
TPU2735-TC18. The logic of these samples is identical
to TPU2735-TC15.
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