displayed correctly). For a complete scrolling of the string, the number of DMA block transfers should be
at least the number of steps. To repeat the complete character string scrolling, the DMA controller should
repeat the blocks transfer. The DMA must write the blocks to the Character Mapping Segments Data
register (CMDATA).
To enable the scrolling of characters string, write a '1' to the Automated Character Mapping Enable bit in
the Control B register (CTRLB.ACMEN); write a '0' to CTRLB.ACMEN and to disable it.
The selected frame counter defines the number of frames before the SLCD triggers a new DMA block
transfer, after each scrolling steps.
Figure 43-28. Characters String Scrolling Examples (NDIG=3)
String=’HELLO’
(string length=5, STEPS=3)
H E L
E L L
String=’HELLO ‘
(string length=8, STEPS=6)
L L O
L O
O
H E L
H E L
E L L
L L O
H E L
1
2
3
1
2
3
1
step
1
2
3
4
5
6
1
E L L
L L O
H E L
Limitations of Auto Character Mapping Mode
If ACM is enabled and the Auto Character Mapping Busy bit in the Status register (STATUS.ACMBUSY)
is asserted, any write access to the Character Mapping Data register (CMDATA) will be considered as
coming from the DMA controller, and therefore handled by the ACM state machine. So if the user
accidentally writes CMDATA in this period, the ACM state machine will be corrupted. Consequently, the
user should not write to the CMDATA register when ACM is active, and make sure that all CMDATA
access is in the period of ACM inactivity.
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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