SLAZ333AC October   2012  – September 2021 MSP430F6635

 

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6.41 SYS18

USB Module

Category

Functional

Function

USB registers are unlocked and ACCVIFG is set at start-up

Description

During device start-up, an incorrect line of code in the start-up code causes the USB registers to remain unlocked and causes an access violation, setting ACCVIFG bit.
In the  BSL430_Low_Level_Init code, the following line of code accesses USBKEY (incorrect register address) instead of USBKEYPID, causing an access violation setting ACCVIFG bit, and leaving the USB registers unlocked.
mov.w   #0x0000,   &USBKEY     ; lock USB

The correct line of code should read:
mov.w   #0x0000,   &USBKEYPID     ; lock USB correctly

Note: This code does not run when using the JTAG debugger - the behavior only appears when running standalone.

Workaround

1. Load the latest version of the USB BSL from Custom BSL Download

OR

2. Load a non-USB or custom BSL

OR

3. Erase the BSL

OR

4. Clear the access violation flag at the beginning of the application code with the following C code (or its assembly equivalent):


USBKEYPID = 0;       // Lock USB correctly
FCTL3 = 0xA558;      // Clear violation flag