MC44002 MC44007
FLAGS RETURNED BY THE MC44002/7
36
MOTOROLA ANALOG IC DEVICE DATA
When the Address Read/Write bit is high the last two bytes
of I2C data are read by the MCU as status flags; a listing of
these may be found in Table 5. The MC44002/7 is designed
to be part of a closed-loop system with the MCU; these flags
are the feedback mechanism which allow the MCU to interact
with the MC44002/7.
A brief description of each of the flags, its significance and
possible uses are given below.
Table 5. Flags Returned
Clock #
Flag (Bit High)
10
Horizontal Flyback Present
11
Horizontal Drive Enabled
12
Horizontal Out Of Lock
13
Excess Average Beam Current
14
Less Than 576 Lines
15
Vertical Countdown Engaged
16
Overload Average Beam Current
17
Reserved
18
(Acknowledge)
19
Grid 2 Voltage Up Request
20
Grid 2 Voltage Down Request
21
OK
22
Fault
23
ACC Active
24
PAL Identified
25
SECAM Identified (MC44002 only)
26
Excess Peak Beam Current
27
(Acknowledge)
Horizontal Flyback Present
–
A sense of the horizontal
flyback is taken via a current limiting series resistor from one
of the flyback transformer secondaries to Pin 13. This is used
for the H-phase shift control, but the presence of the pulse is
also flagged to the MCU. Should the flag be missing after the
chassis has been started up, then the MCU would have to
shut down the set immediately.
Horizontal Drive Enabled
–
Indicates that the horizontal
drive pulse output at Pin 15 has been enabled. This occurs
after the stored values in the nonvolatile memory have been
transferred to the MC44002/7 memory.
Horizontal Out of Lock
–
This flag is high when no valid
signal is being received by the MC44002/7. Possible action in
this case would be to change the phase detector gain and
time constant bits to ensure rapid capture and locking to a
new signal.
Excess Average Beam Current
–
This is one of two
threshold levels which are determined by an external
component network connected to the beam current sensing
at Pin 9. This flag indicates an excess of beam current. A
typical application of this flag in conjunction with “Overload
Average Beam Current” flag is for the software controlled
Automatic Beam Current Limiting. When this flag is “on”, it is
recommended that the software prevent increases to the
Contrast setting.
Less Than 576 Lines
– Output from the line counter in the
vertical timebase. If there is a count of less than 576 this is
indicative of a 525 line system being received. If the flag is
low then a 625 line system is being received. This information
can be used as part of an automatic system selection
software.
Vertical Countdown Engaged
– The vertical timebase is
based on a countdown system. The timebase starts in
Injection Lock mode and when vertical retrace is initiated a
4-bit counter is set to zero. A coincidence detector looks for
counts of 625 lines. In Auto mode each coincidence causes
the counter to count up. When eight consecutive
coincidences are detected, the countdown is engaged. The
MSB of the counter is used to set this flag to the processor.
Overload Average Beam Current
–
This is the second
threshold level which is set by the external component
network on Pin 9. The flag warns of an overload in anode
current which should be lowered by reducing the Contrast.
Grid 2 Voltage Up/Down Requests
– These flags
indicate when the RGB output loops are about to go out of the
control range necessary for correct gray scale tracking.
These 2 flags are used during factory adjustment.
OK and Fault
–
These two flags are included as a check
on the communication line between the MCU and
MC44002/7. The OK flag is permanently wired high and Fault
is permanently wired low. The MCU can use these flags to
verify that the data received is valid.
ACC Active
–
This flag is high when there is a sufficient
level of burst present in PAL and NTSC modes during the
video back porch period. The flag goes low when the level of
burst falls below a set threshold or if the signal becomes too
noisy. The flag is used to implement a software color killer in
PAL and NTSC and is also available for system identification
purposes. Since in SECAM there is line carrier present
during the gating period, it is quite likely that the ACC will be
on, or will flicker on and off in this mode.
* PAL Identified
–
Recognizes the line-by-line swinging
phase characteristic of the PAL burst. When this flag is on
together with the ACC flag, this is positive identification for a
PAL signal.
* SECAM Identified
–
Senses the changing line-by-line
reference frequencies (Fo1 and Fo2) present during the back
porch period of the SECAM signal. This flag alone provides
identification that SECAM is being received (MC44002 only).
Excess Peak Beam Current
–
A voltage threshold is set
on the beam current feedback on Pin 20, which is also used
for the RGB output loops for current sampling. When the
threshold is reached, the flag is set, indicating too high a peak
beam current which may be in only a part of the screen. The
response of the MCU might be to reduce the contrast of the
picture. This flag, together with the Excess Average Beam
Current flag, performs the function of beam limiting. The
exact way in which this is handled is left to the discretion of
the user who will have their own requirements, which may be
incorporated by the way in which the software is written.
* These two flags are set in opposition to one another such that they can never both be on at the same time. This has been done to try to prevent misidentification from occurring. Often it is
very difficult to distinguish between PAL and SECAM especially when broadcast material has been transcoded, sometimes badly, leaving e.g. large amounts of SECAM carrier in a
transcoded PAL signal (also often with noise). With this method the strongest influence will win out making a misidentification much less likely.