C167CS datasheet(315/517 Pages) INFINEON

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C167CS

Derivatives

The Bootstrap Loader

User’s Manual

15-5

V2.0, 2000-07

15.2

Loading the Startup Code

After sending the identification byte the BSL enters a loop to receive 32 Bytes via ASC0.

These bytes are stored sequentially into locations 00’FA40H through 00’FA5FH of the

internal RAM. So up to 16 instructions may be placed into the RAM area. To execute the

loaded code the BSL then jumps to location 00’FA40H, i.e. the first loaded instruction.

The bootstrap loading sequence is now terminated, the C167CS remains in BSL mode,

however. Most probably the initially loaded routine will load additional code or data, as

an average application is likely to require substantially more than 16 instructions. This

second receive loop may directly use the pre-initialized interface ASC0 to receive data

and store it to arbitrary user-defined locations.

This second level of loaded code may be the final application code. It may also be

another, more sophisticated, loader routine that adds a transmission protocol to enhance

the integrity of the loaded code or data. It may also contain a code sequence to change

the system configuration and enable the bus interface to store the received data into

external memory.

This process may go through several iterations or may directly execute the final

application. In all cases the C167CS will still run in BSL mode, i.e. with the watchdog

timer disabled and limited access to the internal code memory. All code fetches from the

internal ROM area (00’0000H … 00’7FFFH or 01’0000H … 01’7FFFH, if mapped to

segment 1) are redirected to the special Boot-ROM. Data fetches access will access the

internal code memory of the C167CS, if any is available, but will return undefined data

on ROMless devices.

Note: Data fetches from a protected ROM will not be executed.

15.3

Exiting Bootstrap Loader Mode

In order to execute a program in normal mode (i.e. watchdog timer active, full access to

user memory, etc.), the BSL mode must be terminated first. The C167CS exits BSL

mode in two ways:

upon a software reset, ignoring the external configuration (P0L.4 or RD)

upon a hardware reset, not configuraing BSL mode.

After the (non-BSL) reset the C167CS will start executing out of user memory as

externally configured via PORT0 or RD/ALE (depending on EA).

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