 10.1 Equivalent Binary Designations: Summary of Equivalence Symbol 1 Symbol 0 Mark or marking Space or spacing Current on Current off Negative voltage Positive voltage Hole (in paper tape) No hole (in paper tape) Condition Z Condition A Tone on (amplitude modulation) Tone off Low frequency (frequency shift keying) High frequency Inversion of phase No phase inversion (differential phase shift keying) Reference phase Opposite to reference phase Source: Ref.2. To a certain extent, this is a review of the argument presented in Section 6.2.3. 10.4 CODING Column 0123456 00000 ESPo@P 01004 NAK5EUe 10008 101111 1101 13 1110 14 Figure 10.1 American Standard Code for Information Interchange (ASCII). [From MiL-STD-188C. Updated (Ref. 26).] 4000000011 30011101 200001 S1010101 0101& 01100 1000 bcdefgh 1001 ikimnopgr Suvwy 1100 ABCDEFGHI 1101 JKLMNOPQR STUVWXY 1111013456789 PF - Punch Off RES Restore BYP Bypass HT - Horiz. Tab NL - New Line LF - Line Feed LC - Lower Case BS - Backspace EOB - End of Block DEL - Delete IL Idle PRE - Prefix SP - Space PN - Punch On RS - Reader Stop UC - Upper Case EOT - End of Transmission SM - Start Message Figure 10.2 The extended binary-coded decimal interchange code (EBCDIC). DATA COMMUNICATIONS or four pieces of information, and each can be assigned a meaning such as 1, 2, 3, 4 or A, B, C, D. Suppose three bits are transmitted in sequence. Now there are eight possibilities: We could continue this argument to sequences of four bits, and it will turn out that there are now 16 different possibilities. It becomes evident that for a binary code, the number of distinct characters available is equal to two raised to a power equal to the number of elements (bits) per character. For instance, the last example was based on a four-element code giving 16 possibilities or information characters (i.e., 24 = 16). The classic example is the ASCII code, which has seven information bits per char- acter. Therefore the number of different characters available is 27 = 128. The American Standard Code for Informa