Controlling Protocol ......
Store and Play Speech
Speech Store Commands
62
H
63
H
STORE ‘N’ PAGES – START PAGE ‘X’
(immediate).
STORE ‘N’ PAGES – START PAGE ‘X’
(buffered).
The IRQ output is cleared by reading the Status Register.
61
H
READ STATUS REGISTER
(Table 6).
The digitised speech from the Delta Encoder is stored
in consecutive DRAM locations with the Speech Store
Counters sequencing through the DRAM addresses and
counting the number of complete ‘pages’ stored since the
start of execution of the command.
As soon as the command has terminated the following
events take place:
(1) The “Store Command Complete” bit in the Status
Register (Table 6) is set.
(2) An “Interrupt Request” (IRQ) is sent (if enabled) to
the
µC.
(3) The next Speech Store command (if present) is
immediately taken from the Store Command
Buffer and execution of the new command
commences.
Speech Playback
is controlled by similar commands:
64
H
65
H
PLAY ‘N’ PAGES – START PAGE ‘X’
(immediate).
PLAY ‘N’ PAGES – START PAGE ‘X’
(buffered).
To provide continuity of speech commands, both Store
and Play commands can be presented to the FX802 in
one of two formats;
Immediate or Buffered.
An
Immediate
command will be started on completion
of its loading, irrespective of the condition of the current
command.
A
Buffered
command will be acted upon on the
completion of the current Store or Play command, unless
Speech Synchronization Bits (Control Register) are set.
Buffering of commands lets the DVSR Codec execute
a series of commands without intervening gaps, even
though the
µController
may take several milliseconds to
respond to each “Command Complete” Interrupt
Request.
In either case, the Store or Play Command Complete
bit of the Status Register will be cleared.
Store/Play Speech Synchronization –
(Table 4)
This facility is provided, primarily, for Time Domain
Scrambling applications.
Speech Synchronization bits in the Control Register
will produce the effects described below:
No Speech Sync Set;
Store and Play operations may
take place completely independently.
Store after Play;
The next “buffered” Store command
will start
on completion of a Play operation,
whilst the
next Play command (if any) sequence continues
normally.
Play after Store;
The next “buffered” Play command will
start
on completion of a Store operation,
whilst the next
Store command (if any) sequence continues normally.
These actions will continue whilst ‘Speech Sync’ bits
remain set.
using the Speech Play Counters and Play Command
Buffer.
As soon as the Play Command has completed, the
“Play Command Complete” bit in the Status Register is
set and an Interrupt Request generated (if enabled).
If no 'next' command is waiting in the Play Command
Buffer when a speech Play command finishes,
a continuous idle code (0101.....0101) will be fed to the
Delta Decoder.
Speech “data” is stored or recovered at the selected
Encode or Decode sample rate (Table 3).
Store or Play Command Complete bits in the Status
Register are cleared by the next Store or Play command
received from the
µC,
or by a General Reset command.
DRAM Speech Capacity
28-pin/lead versions of the FX802 may be used with a single 256kbit DRAM or with up to 4 x 1Mbit 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 2 gives information on storage capacity and Store/Playback times. Speech data can be replayed at a different
sample rate or in a reverse sequence, see Control Register for details.
DRAM
Size
256kbits
1024k
2Mbits
3M
4M
Available
Bits
262144
1048576
2097152
3145728
4194304
“Speech
Pages”
256
1024
2048
3072
4096
16
16.0
65.0
131.0
196.0
262.0
Nominal Sample Rates (kbits/s)
25
32
50
10.0
42.0
84.0
126.0
168.0
8.0
32.0
65.0
98.0
131.0
5.0
20.0
42.0
63.0
84.0
64
4.0
16.0
32.0
49.0
65.5
Store and Play Times (seconds)
Table 2 Sampling Clock Rates vs Speech Storage/Playback Times
6
CMLMICRO [ CML MICROCIRCUITS ]
