
UM10800
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User manual
Rev. 1.2 — 5 October 2016
274 of 487
NXP Semiconductors
UM10800
Chapter 16: LPC82x SCTimer/PWM
Writing to the COUNT_L, COUNT_H, or unified register is only allowed when the
corresponding counter is halted (HALT bits are set to 1 in the CTRL register). Attempting
to write to the counter when it is not halted causes a bus error. Software can read the
counter registers at any time.
16.6.9 SCT state register
Each group of enabled and disabled events is assigned a number called the state
variable. For example, a state variable with a value of 0 could have events 0, 2, and 3
enabled and all other events disabled. A state variable with the value of 1 could have
events 1, 4, and 5 enabled and all others disabled.
Remark:
The EVm_STATE registers define which event is enabled in each group.
Software can read the state associated with a counter at any time. Writing to the
STATE_L, STATE_H, or unified register is only allowed when the corresponding counter is
halted (HALT bits are set to 1 in the CTRL register).
The state variable is the main feature that distinguishes the SCTimer/PWM from other
counter/timer/ PWM blocks. Events can be made to occur only in certain states. Events, in
turn, can perform the following actions:
•
set and clear outputs
•
limit, stop, and start the counter
•
cause interrupts and DMA requests
•
modify the state variable
The value of a state variable is completely under the control of the application. If an
application does not use states, the value of the state variable remains zero, which is the
default value.
A state variable can be used to track and control multiple cycles of the associated counter
in any desired operational sequence. The state variable is logically associated with a state
machine diagram which represents the SCT configuration. See
and
for more about the relationship between states and events.
The STATELD/STADEV fields in the event control registers of all defined events set all
possible values for the state variable. The change of the state variable during multiple
counter cycles reflects how the associated state machine moves from one state to the
next.
If UNIFY = 1 in the CONFIG register, only the _L bits are used.
Table 229. SCT counter register (COUNT, address 0x5000 4040) bit description
Bit
Symbol
Description
Reset
value
15:0
CTR_L
When UNIFY = 0, read or write the 16-bit L counter value. When
UNIFY = 1, read or write the lower 16 bits of the 32-bit unified
counter.
0
31:16
CTR_H
When UNIFY = 0, read or write the 16-bit H counter value. When
UNIFY = 1, read or write the upper 16 bits of the 32-bit unified
counter.
0