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Sync
Unlike the 1527, the Sync of 2262 locates at the end of the packet. The Sync pattern is shown below:
1 SYM
31 SYM
Figure 37. 2262 Sync Pattern
During the reception, the CMT2250A dynamically detects the pattern of the Sync to identify whether a 2262 packet is coming. In
some circumstances, the 31 consecutive 0 (low symbols) can bring challenges into the demodulation and bit synchronization.
Because the 31 zeros come along with some data rate offsets can lead to incorrect counting of the number of zeros during the
reception of the Sync. As a result, the device failed to recognize the packet.
To avoid this happening, the CMT2250A allows the user to introduce some tolerance of detecting these 31 low symbols. This
means the device does not necessarily capture 1 high symbol followed by 31 low symbols to identify this is a valid 2262 Sync. For
example, if +/- 13 symbols of detecting tolerance is introduced to the device, 1 high symbol followed by 18 – 44 symbols can
represent a valid 2262 Sync.
5.1.8 2262 Bit Format
In 2262 packet, a single bit is constructed by 8 symbols, as shown below. Please note that only the Address (Sync ID) field and
the Data field have the unit of “bit”. In the below diagram, 1 OSC clock cycle is notated as 1
α referring
to the original 2262 timing
descriptions.
3 SYM
(12
α
)
1 SYM
(4
α
)
3 SYM
(12
α
)
1 SYM
(4
α
)
Bit 1
3 SYM
(12
α
)
1 SYM
(4
α
)
Bit 0
3 SYM
(12
α
)
1 SYM
(4
α
)
3 SYM
(12
α
)
1 SYM
(4
α
)
Bit f
3 SYM
(12
α
)
1 SYM
(4
α
)
Figure 38. 2262 Bit Format Options
5.2 Pulse Mode, Pulse Time
If the pulse mode is turned on, the data pins will retain their values for the time T which is defined by the “Pulse Time” then reset
to their default values. The default values of the data pins are all 1. If the pulse mode is turned off, the 4 data pins DATA0 –
DATA3 are sustained until a new data is received.
Please note that, within the data field D0 – D3 in the packet, logical 1 tells the device to connect the corresponding data output
pin to GND. For example, if the received D0 – D3 is 1001, the logical levels of the DATA0 – DATA3 are 0110.
The following figures show the different DATA0 – DATA3 status after receiving a packet for the situations that the Pulse Mode is
turned on and off. The packet contains a data field which is 1001.
