TC1796
Peripheral Units (Vol. 2 of 2)
Synchronous Serial Interface (SSC)
User’s Manual 20-18 V2.0, 2007-07
SSC, V2.1
20.1.2.9 Baud Rate Generation
The serial channel SSC has its own dedicated 16-bit baud rate generator with 16-bit
reload capability, allowing baud rate generation independent of timers. In addition to
Figure 20-2, Figure 20-9 shows the baud rate generator of the SSC in more detail.
Figure 20-9 SSC Baud Rate Generator
The baud rate generator is clocked with f
SSC
. The timer counts downwards. Register BR
is the dual-function Baud Rate Generator/Reload register. Reading BR while the SSC is
enabled returns the contents of the timer. Reading BR while the SSC is disabled returns
the programmed reload value. In this mode, the desired reload value can be written to
BR.
Note: Never write to BR while the SSC is enabled.
The formulas below calculate either the resulting baud rate for a given reload value, or
the required reload value for a given baud rate:
(20.1)
BR_VALUE represents the content of the reload register, taken as an unsigned 16-bit
integer, while Baud rate
SSC
is equal to f
SCLK
as shown in Figure 20-9.
The maximum baud rate that can be achieved with f
SSC
= 75 MHz is 37.5 Mbit/s in
Master Mode (with BR_VALUE = 0000
H
) and 18.75 Mbit/s in Slave Mode (with
BR_VALUE = 0001
H
).
Table 20-1 lists some possible baud rates together with the required reload values and
the resulting bit times, assuming a module clock f
SSC
of 75 MHz.
MCA05784
16-Bit Counter
16-Bit Reload Register
f
SCLK
f
SSC
/ 2
f
SCLK max
in master mode ≤
f
SSC
/ 4
f
SCLK max
in slave mode ≤
f
SSC
2
Baud rate
SSC
f
SSC
2 BR_VALUE 1+()×
-------------------------------------------------------=
BR_VALUE
f
SSC
2 Baud rate
SSC
×
--------------------------------------------
1–=
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