Programming the Local Host
Chapter 5
58
Figure 5.5
General Command Rung
027
07
AAA
XX
Refer to
Figure 5.6 & Figure 5.7
Start Bit
Remote Station
Command Code
0X Supervisory
00
01
02
03
04
05
06
07
Protected Write Block with Reply
Read Block
Protected Write Bit with Reply
Unprotected Write Block w/Reply
Unprotected Write Bit with Reply
Protected Write Block VERIFIED
Protected Write Bit VERIFIED
Unused
1X TimeCritical
10
11
12
13
14
15
16
17
Protected Write Block with Reply
Read Block
Protected Write Bit with Reply
Unprotected Write Block w/Reply
Unprotected Write Bit with Reply
Protected Write Bit NO REPLY
Protected Write Bit NO REPLY
Unused
Whereas:
Protected means that when a command with this quality is received, it is
checked against the memory access rungs.
Unprotected means that a command with this quality overrides any
memory access rungs put in to stop it. As in Data Highway, they should
be used with discretion.
Memory access does not apply to READ commands, so the READ
BLOCK is neither protected nor unprotected.
Note that Codes 05 and 06 are different from 15 and 16, while other
commands are symmetrical. They are “enhanced” WRITE commands. A
VERIFIED command is issued for supervisory while a NO REPLY
command is issued for time-critical. There is no supervisory NO REPLY,
nor is there a time-critical VERIFIED.
Should you receive Error Code E9, UNKNOWN COMMAND CODE,
(error codes are listed in both this chapter and Chapter 6), it means that
you may have used a command code that is not yet implemented. These
currently include: 03, 04, 05, 06, 13, 14 and unused Command Codes 07
and 17.
