VSR CODEC with DRAM CONTROL
7
MX812 PRELIMINARY INFORMATION
© 1997 MX
•COM Inc.
www.mxcom.com Tele: 800 638-5577 910 744-5050
Fax: 910 744-5054
Doc. # 20480076.003
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
All trademarks and service marks are held by their respective companies.
The Controlling System ......
Status Bits
Received from 812 First
Interrupt Condition (Flag)
Bit 6 or 5 set to a “1”
Cleared condition
Command Buffer
Buffer Empty
Cleared condition
Device Condition
Idle
Storing, Playing or Waiting
Input Power Level
Reading
MSB
7
1
0
6
1
0
5
1
0
43210
Table 3 Status Register
“Read Status Register” – A/C 61
H, followed by 1 byte of Reply Data.
Interrupt Condition (Flag)
– IF
Set to a logic “1” whenever Bit 6 or Bit 5 goes from “0” to
“1” (unless the transition is caused by a General Reset
command 01
H). This indication allows monitoring by ‘poll’
while Interrupts are disabled.
Cleared to a logic “0” by a General Reset command or
immediately following a read of the Status Register.
Command Buffer Status – MT
Set to a logic “1” when the Command Buffer is empty or
by a General Reset command.
Cleared to a logic “0” by loading a new Store, Play, Wait
commands.
Device Condition – I
Set to a logic “1” when NO Store, Play or Wait command
is being executed or by a General Reset command.
Set to a logic “0” while a Store, Play or Wait command is
being executed.
Encode Input Power Level – POWER
Available in the Encode mode, a 5-bit representation of
the analog signal input level, updated at the end of every
Store or Wait command.
This permits the MX812 to perform a continuous sequence
of Store, Play or Wait commands, without gaps and without
requiring an unduly fast response from the mController.
Note that this Command Buffer can only hold one Store,
Play or Wait instruction, each new command received into this
buffer will overwrite any previously loaded contents.
To Store or Play a sequence of pages the relevant commands
should be loaded with sequential page numbers while observing
the Status Register – Bit 6.
Store/Play/Wait Command Buffer
A buffer used to accept and hold the latest Store, Play or
Wait command received over the C-BUS while the MX812 is
executing the previous command. The Status Register, bit 6,
indicates the condition of this buffer.
When a command is received it is first loaded into this
buffer. If the MX812 is already executing a previously loaded
Store, Play or Wait command the new command will be stored
temporarily in the Command Buffer, from where it will be taken
on completion of the previous command.
For the purposes of storage and replay, the attatched
DRAM is divided into ‘data-pages’ of 1024 bits (1kbit).
One Store/Play command (loaded MSB first) will instruct
the MX812 to store or play (depending upon the setting of the
Mode Register, Bit-3) to or from 1 x 1024 “page” of DRAM.
The Store/Play/Wait command buffer will allow continuity of
“Store/Play Page” – A/C 62
H, followed by 2 bytes of Command Data.
operation.
The particular page selected is identified by the 12 lowest
bits of the 2 x Store/Play bytes as shown below.
If a Store command is loaded and executed whilst the
Codec is “Powersaved” in the Encode mode, the selected
DRAM page will be filled with an idle pattern (“101010.....”).
“Wait” – A/C 63
H,
–– Wait for 1024 bit periods
Causes the MX812 to wait for 1024 bit periods (approximately
16 or 32ms).
If the Codec is set to the Encode mode, a new “Power”
reading that is relevant to the input audio level, will be loaded
into the Status Register at the end of the Wait period.
If the Codec is set to the Decode mode it will ‘Play’ a perfect
idle pattern (“101010..........”) during the Wait period.
DRAM Size
Valid Page Nos
Bit Nos
4Mbit
0 – 4095
0 – 11
1 + 1Mbit
0 – 2047
0 – 10
1Mbit
0 – 1023
0 – 9
Bit Number
MSB – Loaded to MX812 First
Loaded Last – LSB
Bit
15
14
13
12
11
10
987
6543210
Bit
Value
x
x
x
x
211
210
29
28
27
26
25
24
23
22
21
20
Value
Page
“0”
“0”
“0”
“0”
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