Plus RS-232 Manuel d'utilisateur télécharger pdf (Page 143)

Data Encoding and Addressing

Chapter 6

6-6

corresponding place value and add the results of the multiplications.

Figure 6.5 shows the octal representation of the decimal number 239.

Figure 6.5

Octal

Numbers

11101111

11336

1 x 2

= 2

1 x 2

= 1

1 x 2

= 4

0 x 2

= 0

1 x 2

= 1

1 x 2

= 4

1 x 2

= 2

1 x 2

= 1

3 x 8

= 192

5 x 8

= 40

357

= 239

7 x 8

= 7

Order of Transmission

PCs store data in 16-bit (2-byte) words. The bits in these words are

numbered (addressed) 0 through 17 octal, going from right to left within a

word, as follows:

15 14 13 12 11 10 07 06 05 04 03 02 01 0017 16

Bits

PC Word

In PC memory, the words are arranged as shown above. However, when

the KF2 module transmits data over its asynchronous link, it transmits

one byte at a time. The module always transmits the low byte (Bits 00

through 07) of a word before the high byte (Bits 10 through 17) of the

same word. Also, the UART transmits the low bit first within a byte.

Thus, when a PC word is traveling over the asynchronous link, it will look

like this:

00 01 02 03 04 05 06 07 10 11 12 13 14 15 16 17

Bits

Time

First Byte Second Byte

1 2 ... 138 139 140 141 142 143 144 145 146 147 148 ... 234 235

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