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M
N
T
T
fe re n c e
R e
In p u t
Instruction Set
952
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
High-End Timer (N2HET) Module
20.6.3.19 RCNT (Ratio Count)
Syntax
RCNT {
[brk={OFF | ON}]
[next={label | 9-bit unsigned integer}]
[control={OFF | ON}]
divisor={25-bit unsigned integer}
[data={25-bit unsigned integer]
}
Figure 20-174. RCNT Program Field (P31:P0)
31
26 25
23
22
21
13 12
9
8
7
6
5
4
3
1
0
0
Reserved
BRK
Next program address
1010
Res.
00
Step
width
Res.
1
6
3
1
9
4
1
2
2
3
1
Figure 20-175. RCNT Control Field (C31:C0)
31
27
26
25
24
0
Reserved
Control
Res.
Divisor
5
1
1
25
Figure 20-176. RCNT Data Field (D31:D0)
31
7
6
0
Data
Reserved
25
7
Cycles
Two Cycles (One Cycle if T=0)
Register modified
None
Description
RCNT is used with other instructions to convert an input period measurement
T
Input
to the form of (
) where the input period is expressed as a
fraction of a reference period T
Reference
.
(31)
RCNT computes the numerator N of (
). The denominator M of
) is a constant that is of interest. For example, choosing M = 100
allows the input period to be expressed as a percentage (%) of the reference
period. Note that if T
Input
> T
Reference
, then RCNT will return N > M ; which would
be correct if, for example, the input pulse period is 110% of the reference
pulse period.
RCNT expects that register T is loaded with the value of T
Reference
. The input
period T
Input
is determined by counting the number of loop resolution periods
between edges on the input pin. This information is conveyed through the Z
flag from a PCNT instruction that precedes the RCNT instruction.
The divisor field of the RCNT instruction should be chosen as:
Divisor = M ·
lr
, where M is the desired denominator from
) and lr is the loop resolution prescale value.
