Installation guide

6: Programming Considerations
DC 900-1564A 87
6.4.2.2 Link Characteristics Identifier (LCI)
The link characteristics identifier field is required in each SLC message sent or received
on a low-level SLC network. Shown as the
lci field in Figure 6–1 on page 86, the LCI
appears as the first byte in the data area of each
DLI_PROT_SEND_NORM_DATA or
DLI_PROT_SEND_PRIOR_DATA command or response. Table 6–1 shows the internal for-
mat of the LCI field. See also the
slc_blks.h “C” include file.
6.4.2.3 Additional Characteristics Indicator (ACI)
The additional characteristics indicator field is optional in each SLC message sent and
received on a low-level SLC network. If the
LCI_ACI_PRESENT bit is set in the lci field,
then the ACI is present, and occupies the leading portion of the
info field shown in
Figure 6–1 on page 86. When present, the ACI and any ACI Extensions have the effect
of reducing the maximum message length. Table 6–2 shows the internal format of the
aci field; each extension of the ACI has the same format.
Table 6–1: Link Characteristics Identifier (LCI) on Low-level Networks
Link Characteristics Identifier (LCI) — One Character
LCI_BASE_VALUE Always set
LCI_PDM Possible Duplicate Message (PDM) when set
LCI_ACI_PRESENT Additional Characteristics Identifier (ACI) present when set
LCI_HLD_PRESENT Always zero (High Level Designators HEX/HEN absent)
LCI_PROTECTION_MASK Mask to isolate (&) or ignore (&~) Protection bit-field
LCI_FULL_PROTECTION Protection bit-field value
LCI_LIMITED_PROTECTION Protection bit-field value
LCI_NO_PROTECTION Protection bit-field value
LCI_LAST_BLOCK Always set (to indicate entire message present)