
Programmable Four-Channel Communications Controller
—
CD2481
Datasheet
65
Transmit and receive data can be encoded and decoded in NRZ, NRZI, or Manchester formats. For
NRZI, at the start of transmission, a learning data stream of contiguous zeros achieves bit
synchronization; for Manchester, an alternating pattern of ones and zeros is required.
NRZ, NRZI, and Manchester
—
Data encoding schemes used in various synchronous protocols. In
NRZ, the signal condition represents the data type, high for a logic 1 and low for a logic 0. In NRZ
and NRZI type of encoding, the transitions of the data stream occur at the beginning of the bit cell.
In NRZI, the signal condition switches to the opposite state to send a binary 0. In Manchester
encoding, the transitions are always in the middle of the bit cell. A high-to-low transition is made
to send a logic 1, and a low-to-high transition to send a logic 0. The following timing diagrams
illustrate the encoding method. The data bits are 0110010.
Example 3
This example illustrates programming the Digital Phase locked loop at 128 kbps in NRZI mode
using the internal clock, at a system clock frequency of 35 MHz.
Divisor loaded into R/TBPR = 33 or 21h
Value loaded into RCOR = 28h, to enable the DPLL, NRZI framing and select clk0.
Example 4
This example illustrates programming the Digital Phase locked loop in the
×
1 External Clock
mode, with Manchester encoding.
Divisor loaded into RBPR = 01h, to enable
×
1 external clock
Value loaded into RCOR = 36h, to enable the DPLL, select Manchester framing, and external
clock.
3600
81
clk2
0.16%
4800
61
clk2
0.35%
7200
40
clk2
0.16%
9600
40
clk1
0.16%
19200
81
clk0
0.35%
38400
40
clk0
0.16%
56000
2c
clk0
0.05%
57600
81
clk0
0.16%
64000
26
clk0
0.16%
76800
61
clk0
0.35%
115200
40
clk0
0.16%
128000
3a
clk0
0.69%
134400
37
clk0
0.35%
150000
31
clk0
0.00%
230400
20
clk0
1.38%
Table 8. Bit Rate Constants, CLK = 60 MHz
(Sheet 2 of 2)
Bit Rate
Divisor
Clock
Error