MITSUBISHI MICROCOMPUTERS
M37274EFSP
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER with CLOSED CAPTION DECODER
and ON-SCREEN DISPLAY CONTROLLER
(7) Start Bit Detecting Circuit
This circuit detects a start bit at line decided in the data slice line
specification circuit. For start bit detection, it is possible to select one
of the following two types by using bit 1 of clock run-in register 2
(address 00E716).
1
After the lapse of the time corresponding to the set value of the
start bit position register (address 00E116), the first rising of the
composite video signal is detected as a start bit.
The time is set in bits 0 to 6 of the start bit position register (address
00E116) (refer to Figure 40). Set a value fit for the following
conditions.
Figure 40 shows the structure of the start bit position register.
Time from the falling of the horizontal
synchronizing signal to the last rising
of the clock run-in
4 ✕ set value of the start bit position
register ✕ reference clock period
Time from the faling of the horizontal
synchronous signal to occurrence of
the start bit
<
<
Start Bit Position Register
b7 b6 b5 b4 b3 b2 b1 b0
Start bit position register (SP) [Address 00E116
]
R
R
W
W
B
Name
Functions
After reset
0
0
to
6
Start bit generating time
(SP0 to SP6)
Time from a falling of the horizontal
synchronous signal to occurrence
of a start bit =
4 ✕ set value (“0016” to “7F16”) ✕
reference clock period
7
0
R
W
DSC1 bit 7 control bit
(SP7)
0 : Generation of 16 pulses
1 : Generation of 16 pulses and
detection of clock run-in
pulse (4 to 6 pulses)
Fig. 40. Start Bit Position Register
45
RENESAS [ RENESAS TECHNOLOGY CORP ]
