
The bootstrap loader
UM0404
DocID13284 Rev 2
15.4.2
Entering the CAN bootstrap loader
The ST10F276 enters BSL mode, if pin P0L.4 is sampled low at the end of a hardware
reset. In this case the built-in bootstrap loader is activated independent of the selected bus
mode. The bootstrap loader code is stored in a special Test-Flash, no part of the standard
mask ROM or Flash memory area is required for this.
After entering BSL mode and the respective initialization the ST10F276 scans the
CAN1_TxD line to receive the following initialization frame:
•
standard identifier = 0h
•
DLC = 0h
As all the bits to be transmitted are dominant bits, a succession of 5 dominant bits and 1
stuff bit on the CAN network is used. From the duration of this frame it calculates the
corresponding baudrate factor with respect to the current CPU clock, initializes the CAN1
interface accordingly, switches pin CAN1_TxD to output and enables the CAN1 interface to
take part in the network communication. Using this baudrate, an Message Object is
configured in order to send an acknowledge frame. The ST10F276 will not send this
Message Object but the host can request it by sending remote frame.
The acknowledge frame is the following for the ST10F276:
•
standard identifier = E6h
•
DLC = 3h
•
Data0 = D5h, that is, generic acknowledge of the ST10 devices
•
Data1 = IDCHIP least significant byte
•
Data2 = IDCHIP most significant byte
For the ST10F276, IDCHIP = 114Xh.
Note:
Two behaviors can be distinguished in the acknowledging of the ST10 to the host. If the host
is behaving according to the CAN protocol, as at the beginning the ST10 CAN is not
configured, the host will be alone on the CAN network and will not get any acknowledge. It
will automatically resent the zero frame. As soon as the ST10 CAN will be configured, it will
acknowledge the zero frame. The “acknowledge frame” with identifier 0xE6, will be
configured, but the Transmit Request will not be set. The host can request this frame to be
sent, and therefore get the IDCHIP, by sending a remote frame.
Flash programming software now knows immediately the exact type of device to be
programmed. as the IDCHIP is sent in the acknowledge frame.