ISD3900
Publication Release Date: Dec 10, 2013
- 28 -
Revision 1.5
imperative that the RVSD has s
et and maintained at “0”. Otherwise, there is a risk that the
User Data may be over-written by subsequent recordings.
8.4
D
IGITAL
A
CCESS OF
M
EMORY
ISD3900 memory can be accessed as conventional digital memory using the DIG_READ and
DIG_WRTIE SPI commands. This allows the user to:
Reserve areas of memory for use as digital non-volatile memory as User Data
Update Voice Prompts and macros (pre-recorded audio) in system.
Read and verify Voice Prompt memory.
Read sector headers of memory to determine memory usage.
The digital read and write commands can be issued even while an audio record or playback is in
progress. The RDY/BSYB pin governs the flow control for all digital operations.
8.5
D
EVICE
E
RASE
C
OMMANDS
ISD3900 provides several ways to erase the flash memory. The flash memory has a minimum
erasable sector size of 4kBytes. The sector erase command is sent with a start and stop sector
address. The ISD3900 also has commands to mass erase the memory.
8.6
M
EMORY
C
ONTENTS
P
ROTECTION
Under certain circumstances, it is desirable for the users to protect portions of the external memory
from write/erase or interrogation (read). The ISD3900 provides a method to achieve this by setting a
protection memory pointer (PMP) that allows the users to protect external memory for an address
range from the beginning of memory to this sector where PMP is pointed. The type of protection is
set by three bits in the memory header byte.
The
CEP
(Chip Erase Protect)
bit set to zero enables chip erase protection. This prevents a
mass erase function, allowing the device to be configured as a write-once part. With the
CEP
bit set to one, even with write protection enabled, the part can be mass erased. After mass
erasure, the initial sector byte defaults to no protection so the device can be re-programmed.
The
WP
(Write Protect) bit set to zero enables write protection of the external memory below
the sector pointed to by the PMP. Write protection means that digital write or erase
commands will not function in this memory area. This can be used to ensure that audio or data
is not inadvertently erased or overwritten. The
WP
bit does not stop the execution of a
REC_MSG@ or ERASE_MSG@ to messages with BOM headers in this memory.
The
RP
(Read Protect) bit set to zero enables read protection of the external memory below
the sector pointed to by the PMP. Read protection means that digital read or audio playback
commands through SPI or I
2
S will not function in this memory area. This can be used to
ensure that external memory contents cannot be digitally copied or read.
Memory protection is activated on power-up of the chip. Therefore, each time the user changes the
setting of memory protection, the new setting will not be effective until the chip is reset.