GMSK Packet Data Modem and RF Transceiver
CMX990
5.1.4.6 Data Quality Register
Data Quality Register $02
Read
7
6
5
4
3
2
1
0
Bit:
Data Quality Reading (0-255)
This is intended to indicate the quality of the receive signal during a Mobitex Data Block or 30
single bytes. In receive mode, the modem measures the ‘quality’ of the received signal by
comparing the actual received zero crossing time against an internally generated time. This
value is averaged over 240 bits and at the end of the measurement the Data Quality Register
and the DQRDY bit in the Status 1 Register is updated. Note: An interrupt will only occur at
this time if the Enable DQ IRQ bit = ‘1’.
To provide synchronisation with Data Blocks, and hence ensure the Data Quality Register is
updated in preparation to be read when the RDB task finishes, the measurement process is
reset at the end of tasks SFH, SFS, RDB and R3H.
In transmit mode all bits of the Data Quality Register will be ‘0’.
Figure 17 shows how the value (0-240) read from the Data Quality Register varies with
received signal to noise ratio.
Figure 17 Typical Data Quality Reading (after 240 bits) vs baseband S/N
(noise in bit rate bandwidth)
ã 2004 CML Microsystems Plc
36
D/990/1
CMLMICRO [ CML MICROCIRCUITS ]
