Zilog Z16C35 User Manual

Page 62

ISCC

User Manual

UM011002-0808

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 change 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

Select sync character length

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