
ISCC
User Manual
UM011002-0808
56
modem that encodes or decodes clock information in the modulation process. Refer to the
Monosync message format as shown in Figure 4-4.
The Bisync mode of operation is similar to the Monosync mode, except that two sync
characters are provided instead of one. Bisync attempts a more structured approach to syn-
chronization through the use of special characters as message “headers”
or “trailers”.
External Sync mode eliminates the use of sync characters in the
serial data stream by pro-
viding an external sync signal to mark the beginning of a data field; i.e., an external input
pin (Sync) waits for an active state c
hange to indicate the beginning of an information
field.
Character-oriented mode is selected by programming bits D3 and D2 of WR4 with zeros.
This selects synchronous mode
, as opposed to asynchronous mode, but this selection is
further modified by bits 5 to 7 of WR4 as well as bits 1 and 0 of WR10. In sync character-
oriented modes, except External Sync mode, the state of bits 7 and 6 of WR4 are always
forced internally to zeros. In external sync mode, these two bits must be programmed as
described in Section 5.4.5.
Table 4–13. Registers Used in Character-oriented Modes
Register Bit No Description
WR4 3 (=0) Select sync mode
2 (=0)
4 (=0) Select monosync mode
5 (=0) (8-bit sync character)
4 (=1) Select bisync mode
5 (=0) (16-bit sync character)
4 (=1) Select external sync mode
5 (=1) (external sync signal required)
6 (=0) Select 1x clock mode
7 (=0)
WR6 7-0 Sync character (low byte)
WR7 7-0 Sync character (high byte)
WR10 1 Select sync character length
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