PRELIMINARY ISD1700 SERIES
Publication Release Date: Nov 6, 2008
- 29 -
Revision 1.31
: Play : Record : Erase
Erasable
Non-erasable
1
1
2
3
1
2
3
4
1
2
1
2
3
4
2
3
4
2
3
(Null)
FF
10
1
2
3
4
X
2
3
4
RECORD
RECORD
RECORD
RECORD
FWD x 3
ERASE
FWD x 2
ERASE
FWD x 2
: Play : Record : Erase
Erasable
Non-erasable
1
1
1
2
3
1
2
3
1
2
3
4
1
2
3
4
1
2
1
2
1
2
3
4
1
2
3
4
2
3
4
2
3
4
2
3
2
3
(Null)
FF
10
(Null)
FF
10
1
2
3
4
X
2
3
4
RECORD
RECORD
RECORD
RECORD
FWD x 3
ERASE
FWD x 2
ERASE
FWD x 2
Figure 9.1 Circular Memory Management
An example of the Circular memory management is shown in Figure 9.1. Here the memory array
starts with an empty memory, the ISD1700 detects this and sets the record pointer to point at row
0x010, the first row of normal memory. A subsequent REC command will record message 1. Now the
playback pointer will point to the beginning of message 1 and the record pointer to the next row after
message 1. Three more recordings will write message 2, 3 and 4. This results the record and
playback pointers are at next row after message 4 and beginning of message 4, respectively. If two
FWD commands are now sent, the playback pointer will jump from last message to message 1 then
message 2. Note that the erase pointer is now invalid since erase is restricted to only the first or last
message. If three FWD commands were executed, the playback pointer would end up back at
message 1 after wrapping around the last message. Because the pointer is at the first message an
erase command is valid. An ERASE will remove message 1 from the memory. Note that the record
pointer has been unaffected by all these operations. A further two FWD and a subsequent ERASE
commands will remove message 4.
