TMP92FD54AI datasheet(51/84 Pages) TOSHIBA

51 / 84 page

2006-01-27

92FD54AI-51

TMP92FD54AI

8) Calculating SUM

SUM is word value which the boot program returns after summing the values of all

the data bytes which it has read. The resulting SUM is sent to the controller high-order

byte first and low-order byte last. All the data in the flash memory (512 K-bytes) is

included in the calculation of SUM. The following example illustrates how the flash

memory SUM command calculates the SUM value which is returned.

Example:

9) Calculating CHECKSUM

CHECKSUM is obtained by taking the 2’s-complement of the unsigned 8-bit value

obtained by summing the values of the bytes received, ignoring any overflow. The

CHECKSUM returned when the Flash Memory SUM command or Product

Information Read command is executed is calculated in this way. The controller should

also use this calculation method when transmitting CHECKSUM values.

Example: Calculating CHECKSUM for Flash Memory SUM command

In this example the CHECKSUM value is found for when the high-order byte of

SUM is E5H and the low-order byte is F6H.

First, the bytes are summed to yield an unsigned result.

E5H

+ F6H = 1DBH

Take the 2s complement of the low-order byte of the resulting value as shown

below. The result is the CHECKSUM value. Consequently, the value 25H is sent

to the controller.

− DBH = 25H

A1H

B2H

C3H

D4H

When the calculation is performed on the four data

entries shown on the left, the value of SUM is:

A1H

+ B2H + C3H + D4H = 02EAH

Hence the high-order data value for SUM is 02H and

the low-order data value is EAH. Therefore SUM is sent

to the controller as the value 02H followed by the value

EAH.

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