DVSR CODEC
11
MX802
4.1.4.3 Write Data
4.1.4.3.1 66 WRITE DATA -- START PAGE “P”
H
This command sets the Data Write Counter to “P” page, and then writes data bytes to successive DRAM
locations, incrementing the Data Write Counter by 1 for each bit received via the C-BUS.
The Start Page, “P,” is indicated by loading a 2-byte word after the relevant Address/Command byte. This 16-
bit word allows data page addresses from 0 to 65535 (4Mbits DRAM).
4.1.4.3.2 68 WRITE DATA CONTINUE
H
This command writes data bytes to successive DRAM locations determined by the Data Write Counter,
incrementing the counter by 1 for each bit received over the C-BUS.
4.1.4.4 DRAM Speech Capacity
28-pin/lead versions of the MX802 may be used with a single 256kbit DRAM, or with up to 4 x 1Mbit of
DRAM. 24-pin/lead versions may only be used with a single 256kbit or 1Mbit DRAM. The different encode
and decode sampling clock rates available enable the user to set voice store and play times against
recovered speech quality. Table 4 gives information on storage capacity and Store/Playback times. Speech
data can be replayed at a different sample rate or in a reversed sequence (see Control Register for details).
DRAM Size Available bits Speech Pages
Nominal Sample Rates (kbps)
16
25
32
50
64
256kbps
1024kbps
2Mbps
262144
256
16.0
65.0
131.0
196.0
262.0
10.0
42.0
84.0
126.0
168.0
8.0
5.0
4.0
1048576
2097152
3145738
4194304
1024
2048
3072
4096
32.0
65.0
98.0
131.0
20.0
42.0
63.0
84.0
16.0
32.0
49.0
65.5
3Mbps
4Mbps
Table 4: Sampling Clock Rates vs. Speech Storage/Playback Times
4.1.4.5 Encoder and Decoder Sampling Clocks
Encoder and decoder sampling clock rates are programmable via the Control Register. Table 5 shows the
range of sampling rates available for different Xtal/clock input frequencies and the counter ratios used to
produce them. Consideration should be given to the effect of different Xtal/clock frequencies upon the audio
frequency performance of the device.
Control Register
Byte 0, Bits
Internal Counter
Division Ratio
Xtal Clock Frequency (MHz)
5
2
0
1
1
1
1
4
1
1
0
0
1
1
3
0
1
0
1
0
1
Dec.
Enc.
4.0
4.032
4.096
256
160
128
80
15.625
25.0
15.75
25.20
31.50
50.4
16.0
25.60
32.0
31.25
50.0
51.20
64.0
64
62.50
63.0
Table 5: Sampling Clock Rates Available
With respect to using a single Xtal/clock frequency for all DBS 800 devices in use, it should be noted that
a. A 4.032MHz Xtal/clock input will produce an accurate 1200-baud rate for the MX809 MSK Modem.
b. A 4.096MHz Xtal/clock input will generate exactly 16kbps, 32kbps and 64kbps Codec sampling clock
rates.
ꢀ1998 MX-COM, Inc.
www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054
Doc. # 20480033.008
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
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