Texas Instruments CC2500 User Manual

CC2500
S
WRS040
C
Page
26
of
89
The
GDO0
pin can also be used for an on
-
chip
analog temperature sensor. By measuring
the
voltage on the
GDO0
pin with an
external ADC,
the temperature can be calculated.
Specifications fo
r the temperature sensor are
found in Section
4.7
on page
14
.
With default
PTEST
register setting (0x7F) t
he
temperature sensor output is only available
whe
n the frequency synthesizer is enabled
(e.g. the MANCAL, FSTXON, RX and TX
states). It is necessary to write 0xBF to the
PTEST
register to use the analog temperature
sensor in the IDLE state. Before leaving the
IDLE state, the
PTEST
register should be
restored to its default value (0x7F).
11.3
Optional Radio Control Feature
The
CC2500
has an optional way of controlling
the radio, by reusing
SI
,
SCLK
and
CSn
from
the SPI interface. This feature allows for a
s
imple three
-
pin control of the major states of
the radio: SLEEP, IDLE, RX and TX.
This optional functionality is enabled with the
MCSM0.PIN_CTRL_EN
configuration bit.
State changes are commanded as follows:
When
CSn
is high the
S
I
and
SCLK
is set to
the desired state according to
Table
18
.
When
CSn
goes low the state of
SI
and
SCLK
is
latched and a command strobe is generated
internally according to the control coding. It is
only possible
to change state with this
functionality. That means that for instance RX
will not be restarted if
SI
and
SCLK
are set to
RX and
CSn
toggles. When
CSn
is low the
SI
and
SCLK
has normal SPI functionality.
All pin control command strobes are executed
immediat
ely, except the
SPWD
strobe, which is
delayed until
CSn
goes high.
CSn
SCLK
SI
Function
1
X
X
Chip unaffected by
SCLK
/
SI

0
0
Generates
SPWD
strobe

0
1
Generates
STX
strobe

1
0
Generates
SIDLE
strobe

1
1
Generates
SRX
strobe
0
SPI
mode
SPI
mode
SPI mode (wakes up into
IDLE if in SLEEP/XOFF)
Table
18
: Optional
P
in
C
ontrol
C
oding
12
Data Rate Programming
The data rate used when transmitting, or the
data rate expected in receive is programme
d
by the
MDMCFG3.DRATE_M
and the
MDMCFG4.DRATE_E
configuration registers.
The data rate is given by the formula below.
As the formula shows, the programmed data
rate depends on the crystal frequency
.


XOSC
E
DRATE
DATA
f
M
DRATE
R




28
_
2
2
_
256
The following approach can be used to find
suitable values for a given data rate:
256
2
2
_
2
log
_
_
28
20
2






















E
DRATE
XOSC
DATA
XOSC
DATA
f
R
M
DRATE
f
R
E
DRATE
If
DRATE_M
is rounded to the nearest integer
and becomes 256, increment
DRATE_E
and
use
DRATE_M
=0
.
The data rate can be set from 1.2
kBaud
to
500
kBaud
with the minimum step size of:
Min Data
R
ate
[
kBaud
]
Typical
D
ata
R
ate
[
kBaud
]
Max
D
ata
R
ate
[
kBaud
]
Data Rate
Step S
ize
[
kBaud
]
0.8
1.2/2.4
3.17
0.0062
3.17
4.8
6.35
0.0124
6.35
9.6
12.7
0.0248
12.7
19.6
25.4
0.0496
25.4
38.4
50.8
0.0992
50.8
76.8
101.6
0.1984
101.6
153.6
203.1
0.3967
203.1
250
406.3
0.7935
406.3
500
500
1.5869
Table
19
: Data
R
ate
S
tep
S
ize

Texas Instruments CC2500 Specifications

General

Brand	Texas Instruments
Model	CC2500
Category	Transceiver
Language	English