Bonito Technical Manual
V2.4.0
46
Parameters and commands
Timer prescaler value (K)
The prescaler value is used to divide the basic timer clock frequency of 56 MHz by
a value of (K + 1) down to a smaller clock frequency. The resulting frequency is
utilized as the time base for exposure time
E
and frame duration
F
. This param-
eter is 16 bit wide.
The implementation of this value provides flexibility between the maximum
interval length, the smallest possible resolution, and the size of the numbers
involved.
If the value K is increased while the values E and F stay the same, the real expo-
sure time and frame duration will decrease.
Range
From
1
to
FFFF
(0xFFFF = 65535)
Default
A7
, leading to 3 μs
Related
Parameters
E
,
F
Examples
K=A7
(0xA7 = 167, timer resolution of ((167 + 1) / 56 MHz) = 3 μs)
E=64
(0x64 = 100, sets exposure time to 100 prescaler ticks)
F=FA0
(0xFA0 = 4,000, set frame duration to 4,000 prescaler ticks)
Result:
exposure time: 100 * 3 μs = 300 μs
frame duration = 4,000 * 3 μs = 12,000 μs
K=53
(0x53 = 83, timer resolution of ((83 + 1) / 56 MHz) = 1.5 μs)
E=64
(0x64 = 100, sets exposure time to 100 prescaler ticks)
F=FA0
(0xFA0 = 4,000, set frame duration to 4,000 prescaler ticks)
Result:
exposure time: 100 * 1.5 μs = 150 μs
frame duration = 4,000 * 1.5 μs = 6,000 μs
Exposure control mode (M)
Use parameter
M
to setup the exposure control mode. The exposure control
depends on a number of general timing parameters that are specified in the
table below.
Note
Use
exact multiples
of the current line duration to minimize
exposure and frame-to-frame jitter. (
K=A7
for 3 μs,
K=53
for
1.5 μs)
