Modem SPI Register Descriptions
MC1321x Reference Manual, Rev. 1.6
Freescale Semiconductor
5-7
5.6
TX_Pkt_Ctl - Register 03
The TX_Pkt_RAM_Ctl Register 03 contains two fields that control operation of the two transmit Packet
RAMs. The first field tx_ram2_select, Bit 15, determines which of the transmit Packet RAMs is selected
for present operations. The second field tx_pkt_length, Bits 6-0, defines the length of the payload data for
a transmission data packet.
5.7
CCA_Thresh - Register 04
The CCA_Thresh Register 04 contains the cca_vt[7:0] 8-bit CCA threshold value, Bits 15 - 8. To calculate
desired the cca_vt[7:0] value:
Threshold value = hex (| (Threshold Power in dBm) * 2 |)
A second field is power_comp[7:0], Bits 7 - 0, which is an offset that is divided by 2 and added to the
measured value of the average energy from a CCA/ED function or LQI value from an RX function, and
the resulting value is stored in cca_final[7:0], RX_Status Register 2D. By using this power_comp[7:0]
value, users can compensate the cca_final[7:0] value for external gain in the RX path. See
“Clear Channel Assessment (CCA) Modes (including Link Quality Indication)”
for more detailed
information.
NOTE
The default value for power_comp[7:0] is 0x8D. To center the reported
cca_final[7:0] value over temperature, it is suggested that a value of 0x9B
be written to power_comp[7:0], which equates to a 3.5dBm offset from
default.
Register 03
0x03
BIT
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
tx_ram2_
select
tx_pkt_length[6:0]
TYPE
r/w
r/w
RESET
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0x0000
Table 5-5. Register 03 Description
Name
Description
Operation
Bits 14- 7
Reserved
Leave default
Bit 15
tx_ram2_select
— The Transmit RAM select bit selects between
transmit Packet RAM1 and transmit
Packet RAM2 for operations involving transmit RAM.These include
SPI read, SPI write, packet transmission and software error
interrupts.
1 = tx_ram2_sel
TX Packet RAM2 selected.
0 = tx_ram2_sel
TX Packet RAM1 selected.
Bits 6 - 0
tx_pkt_length[6:0]
— The Transmit Packet Length bits represent
the number of bytes to be transmitted from transmit Packet RAM plus
2 bytes for FCS.
Total transmit payload data length in bytes
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