Specifications

Protocol Definitions

C-8

Table C–1. Clock Speeds at Which Baud Rate Locks

CLKOUT (MHz) CLKIN (MHz)

30 7.5

28 7.0

24 6.0

20 5.0

4.0

C.2.2.2 Data Transfer

Once the communications are synchronized, the actual data transfer is com-

menced. The first two bytes fetched are interpreted as the destination. The

next two bytes fetched are the length. Once the destination is known, a check

is performed to see if the destination lies within B0. If it does, then the bootload-

er will switch the block B0 into program memory and transfer code into B0. Af-

ter this, the user code is transferred to the destination and then a branch is exe-

cuted to the first address of the code. So, as is the case with the SPI, the entry

point of the code must be at the first location for the SCI.

C.2.2.3 SCI Data Transfer Completion

A noteworthy point is the completion of transmission of the SCI data echo.

There can be a character still in transmission when the control is transferred

to the user code. So, if the user code does anything which disturbs the trans-

mission of the SCI, then that last character may be lost. An example is chang-

ing the bit definition of the SCI transmit pin. If this is allowed, the host must take

this fact into account. A second possible option is to incorporate a small delay

in the user code, or perform a SCI check to confirm that the character transmis-

sion is complete.