![](http://datasheet.mmic.net.cn/140000/SPAK56853FG120_datasheet_5015152/SPAK56853FG120_321.png)
Register Descriptions (ESSI0_BASE = $1FFE20, ESSI1_BASE = $1FFE00)
MOTOROLA
Enhanced Synchronous Serial Interface (ESSI)
12-51
Preliminary
12
divide ratio from 1 to 256 (PM = $00 to $FF) can be selected. The bit clock output is
available at the SCK or SC0 clock pins. The bit clock on the ESSI can be calculated from
the peripheral clock value using the following equation:
fFIX_CLK = fIPBus_CLK/4
if DIV4DIS = 0
fFIX_CLK = fIPBus_CLK
if DIV4DIS = 1
fINT_BIT_CLK = fFIX_CLK /[4 x (7 x PSR + 1) x (PM + 1)]
fFRAME_SYN_CLK = (fINT_BIT_CLK)/[(DC + 1) x WL] where DC = DC and WL = 8,
10, 12, or 16
For example if an 8kHz sampling rate is desired, with 8-bit words operating in the Normal
mode, the following parameters can be used:
fIPBus_CLK = fSYSTEM_CLK /2 = 120MHz / = 60mhz
fFIX_CLK = fIPBus_CLK = 60MHz DIV4DIS = 1
fINT_BIT_CLK = fFIX_CLK /[4 x(7 x PSR + 1)x(PM + 1)]
= 60 MHz /[4 x 1 x 117] = 128.2kHz
PS = 0, PM = 116
fFRAME_SYN_CLK = (fINT_BIT_CLK)/[(DC + 1) x WL] DC = 1 = 128kHz/[2 x 8]
= 8.012kHz
The bit clock output is also available internally for use as the bit clock to shift the
Transmit and Receive Shift Registers. Careful choice of the crystal oscillator frequency
and the prescaler modulus allows the telecommunication industry standard codec master
clock frequencies of 2.048MHz and 1.536MHz to be generated; however, such
applications will typically use external clocks and frame syncs. Table 12-17 provides
examples of PM, PSR, and DIV4DIS values available to be used to generate different bit
clocks.
Table 12-17. Chip Clock Rates as a Function of ESSI
Bit Clock Frequency and Prescale Modulus
Frame
Rate
Words/Frame
(DC+1)
Bits/
Word
Bit Clock
Rate
(MHz)
PM PSR FIX_CLK Rate DIV4DIS
IP_CLK Rate1
SYS_CLK
Rate2
8000
32
8
2,048,000
6
0
57,344,000
0
57,344,000
114,688,000
8000
32
8
2,048,000
7
0
65,536,000
0
65,536,000
131,072,000
8000
24
8
1,536,000
8
0
55,296,000
0
55,296,000
110,592,000
8000
24
8
1,536,000
9
0
61,440,000
0
61,440,000
125,880,000
8000
2
10
160,000
10
1
56,320,000
0
56,320,000
112,640,000
8000
2
10
160,000
11
1
61,440,000
0
61,440,000
122,880,000
8000
2
10
160,000
22
0
14,720,000
1
58,880,000
117,760,000
8000
2
10
160,000
92
0
59,520,000
0
59,520,000
119,040,000