AD822 datasheet(33/88 Pages) AD

33 / 88 page

ADuC841/ADuC842/ADuC843

Rev. 0 | Page 33 of 88

User Download Mode (ULOAD)

Figure 39 shows that it is possible to use the 62 kBytes of

Flash/EE program memory available to the user as a single

block of memory. In this mode, all of the Flash/EE memory is

read-only to user code.

However, the Flash/EE program memory can also be written to

during runtime simply by entering ULOAD mode. In ULOAD

mode, the lower 56 kBytes of program memory can be erased and

reprogrammed by user software as shown in

Figure 39. ULOAD

mode can be used to upgrade your code in the field via any user

defined download protocol. By configuring the SPI port on the

part as a slave, it is possible to completely reprogram the

56 kBytes of Flash/EE program memory in only 5 seconds (refer

to Application Note uC007).

Alternatively, ULOAD mode can be used to save data to the

56 kBytes of Flash/EE memory. This can be extremely useful in

data logging applications where the part can provide up to

60 kBytes of NV data memory on chip (4 kBytes of dedicated

Flash/EE data memory also exist).

The upper 6 kBytes of the 62 kBytes of Flash/EE program

memory are programmable only via serial download or parallel

programming. This means that this space appears as read-only

to user code. Therefore, it cannot be accidentally erased or

reprogrammed by erroneous code execution, which makes it

very suitable to use the 6 kBytes as a bootloader.

A bootload enable option exists in the serial downloader to

“always run from E000H after reset.” If using a bootloader, this

option is recommended to ensure that the bootloader always

executes correct code after reset. Programming the Flash/EE

program memory via ULOAD mode is described in more detail

in the description of ECON and in Application Note uC007.

EMBEDDED DOWNLOAD/DEBUG KERNEL

PERMANENTLY EMBEDDED FIRMWARE ALLOWS

CODE TO BE DOWNLOADED TO ANY OF THE

62 kBYTES OF ON-CHIP PROGRAM MEMORY.

THE KERNEL PROGRAM APPEARS AS 'NOP'

INSTRUCTIONS TO USER CODE

USER BOOTLOADER SPACE

THE USER BOOTLOADER

SPACE CAN BE PROGRAMMED IN

DOWNLOAD/DEBUG MODE VIA THE

KERNEL BUT IS READ ONLY WHEN

EXECUTING USER CODE

USER DOWNLOADER SPACE

EITHER THE DOWNLOAD/DEBUG

KERNEL OR USER CODE (IN

ULOAD MODE) CAN PROGRAM

THIS SPACE

FFFFH

2kBYTE

F800H

F7FFH

6kBYTE

E000H

dFFFH

56kBYTE

0000H

62 kBYTES

OF USER

CODE

MEMORY

Figure 39. Flash/EE Program Memory Map in ULOAD Mode

(62 kByte Part)

EMBEDDED DOWNLOAD/DEBUG KERNEL

PERMANENTLY EMBEDDED FIRMWARE ALLOWS

CODE TO BE DOWNLOADED TO ANY OF THE

32 kBYTES OF ON-CHIP PROGRAM MEMORY.

THE KERNEL PROGRAM APPEARS AS 'NOP'

INSTRUCTIONS TO USER CODE

USER BOOTLOADER SPACE

THE USER BOOTLOADER

SPACE CAN BE PROGRAMMED IN

DOWNLOAD/DEBUG MODE VIA THE

KERNEL BUT IS READ ONLY WHEN

EXECUTING USER CODE

USER DOWNLOADER SPACE

EITHER THE DOWNLOAD/DEBUG

KERNEL OR USER CODE (IN

ULOAD MODE) CAN PROGRAM

THIS SPACE

FFFFH

2kBYTE

F800H

F7FFH

NOP'S

8000H

5FFFH

26kBYTE

0000H

7FFFH

8kBYTE

6000H

32 kBYTES

OF USER

CODE

MEMORY

Figure 40. Flash/EE Program Memory Map in ULOAD Mode

(32 kByte Part)

Flash/EE Program Memory Security

The ADuC841/ADuC842/ADuC843 facilitate three modes of

Flash/EE program memory security. These modes can be

independently activated, restricting access to the internal code

space. These security modes can be enabled as part of serial

download protocol as described in Application Note uC004 or

via parallel programming. The security modes available on the

parts are as follows:

Lock Mode

This mode locks the code memory, disabling parallel program-

ming of the program memory. However, reading the memory in

parallel mode and reading the memory via a MOVC command

from external memory is still allowed. This mode is deactivated

by initiating a code-erase command in serial download or

parallel programming modes.

Secure Mode

This mode locks code in memory, disabling parallel program-

ming (program and verify/read commands) as well as disabling

the execution of a MOVC instruction from external memory,

which is attempting to read the op codes from internal memory.

Read/write of internal data Flash/EE from external memory is

also disabled. This mode is deactivated by initiating a code-erase

command in serial download or parallel programming modes.

Serial Safe Mode

This mode disables serial download capability on the device. If

serial safe mode is activated and an attempt is made to reset the

part into serial download mode, i.e., RESET asserted and de-

asserted with PSEN low, the part interprets the serial download

reset as a normal reset only. It therefore cannot enter serial

download mode but can only execute as a normal reset

sequence. Serial safe mode can be disabled only by initiating a

code-erase command in parallel programming mode.

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