AN1177 STMicroelectronics, AN1177 Datasheet - Page 18

• Manufacturer Part Number: AN1177
• Description: P51XA-PSD8XX DESIGN GUIDE
• Manufacturer: STMicroelectronics

AN1177 - APPLICATION NOTE
Express for this second design example, you still do not need to specify any Hex file for the PSD main
Flash memory area. You only need to specify the P51XA linker file(s) for the secondary Flash memory
area (as in the first simple design) because the P51XA will execute code from secondary Flash memory
and download to main Flash memory. See the next subsection for more details.
Memory Map
The boot sequence and memory swap is a four-step process, as shown in Figure 6 to Figure 9.
For more information on both the Page Register and VM Register, see the data sheets and the PSDsoft
Express User Manual .
Memory Map Configuration at Boot-Up. Figure 6 (next page) shows how the memory map looks at
system power-on or at system reset. The “swap” bit is one of the eight internal PSD page register bits,
whose value is zero by default. The “swap” bit is an example of how the page register bits can be imple-
mented for uses other than memory paging. The VM Register controls which space (Program or Data) the
PSD memories appear in and can be set prior to runtime using PSDsoft Express Configuration. The VM
register resides in the PSD and can be accessed at any time by the P51XA. (See the PSD8XX data
sheets.) Here’s what the P51XA does upon power-up or reset:
18/26
Boot from Flash memory boot csboot0 at address 0h
Perform a checksum of main Flash memory
Download main Flash memory from a host computer if needed and validate contents.