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1.
Read
RXBYTES.NUM_RXBYTES
repeatedly at a rate guaranteed to be at
least twice that of which RF bytes are
received until the same value is returned
twice; store value in
2. If n < # of bytes remaining in packet, read
n-1 bytes from the RX FIFO.
3. Repeat steps 1 and 2 until n = # of bytes
remaining in the packet.
4. Read the remaining bytes from the RX
FIFO.
The 4-bit FIFOTHR.FIFO_THR setting is used
to program threshold points in the FIFOs.
Table 29 lists the 16 FIFO_THR settings and
the corresponding thresholds for the RX and
TX FIFOs. The threshold value is coded in
opposite directions for the RX FIFO and TX
FIFO. This gives equal margin to the overflow
and underflow conditions when the threshold
is reached.
A signal will assert when the number of bytes
in the FIFO is equal to or higher than the
programmed threshold. The signal can be
viewed on the GDO pins (see Section 28 on
page 51).
Figure 20 shows the number of bytes in both
the RX FIFO and TX FIFO when the threshold
flag toggles, in the case of FIFO_THR=13.
Figure 19 shows the signal as the respective
FIFO is filled above the threshold, and then
drained below.
53 54 55 56
NUM_RXBYTES
GDO
6
7
NUM_TXBYTES
GDO
Figure 19: FIFO_THR=13 vs. Number of
Bytes in FIFO (GDOx_CFG=0x00 in RX and
GDOx_CFG=0x02 in TX)
21 Frequency Programming
The frequency programming in CC2500 is
designed
to
minimize
needed in a channel-oriented system.
To set up a system with channel numbers, the
desired channel spacing is programmed with
the
MDMCFG0.CHANSPC_M
n.
57
56
55
54
53
8
9
10
9
8
7
6
the
programming
and
SWRS040C
FIFO_THR
Bytes in TX FIFO
0 (0000)
61
1 (0001)
57
2 (0010)
53
3 (0011)
49
4 (0100)
45
5 (0101)
41
6 (0110)
37
7 (0111)
33
8 (1000)
29
9 (1001)
25
10 (1010)
21
11 (1011)
17
12 (1100)
13
13 (1101)
9
14 (1110)
5
15 (1111)
1
Table 29: FIFO_THR Settings and the
Corresponding FIFO Thresholds
Overflow
margin
FIFO_THR=13
56 bytes
FIFO_THR=13
Underflow
margin
RXFIFO
Figure 20: Example of FIFOs at Threshold
MDMCFG1.CHANSPC_E registers. The channel
spacing registers are mantissa and exponent
respectively.
The base or start frequency is set by the 24 bit
frequency word located in the FREQ2, FREQ1
and FREQ0 registers. This word will typically
CC2500
Bytes in RX FIFO
4
8
12
16
20
24
28
32
36
40
44
48
52
56
60
64
8 bytes
TXFIFO
Page 44 of 89
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