Register 2: EPI Main Baud Rate (EPIBAUD), offset 0x004
The system clock is used internally to the EPI Controller. The baud rate counter can be used to
divide the system clock down to control the speed on the external interface. If the mode selected
emits an external EPI clock, this register defines the EPI clock emitted. If the mode selected does
not use an EPI clock, this register controls the speed of changes on the external interface. Care
must be taken to program this register properly so that the speed of the external bus corresponds
to the speed of the external peripheral and puts acceptable current load on the pins. COUNT0 is the
bit field used in all modes except in HB8 and HB16 modes with dual chip selects and quad chip
selects when different baud rates are selected, see page 879 and page 885. If different baud rates
are used, COUNT0 is associated with the address range specified by CS0n and COUNT1 is associated
with the address range specified by CS1. The EPIBAUD2 register configures the baud rates for
CS2n and CS3n.
The COUNTn field is not a straight divider or count. The EPI Clock on EPI0S31 is related to the
COUNTn field and the system clock as follows:
If COUNTn = 0,
kFreqSystemCloceqEPIClockFr
otherwise:
21
2
×
⎟
⎠
⎞
⎜
⎝
⎛
+
⎥
⎦
⎥
⎢
⎣
⎢
=
COUNTn
kFreqSystemCloc
eqEPIClockFr
where the symbol around COUNTn/2 is the floor operator, meaning the largest integer less than or
equal to COUNTn/2.
So, for example, a COUNTn of 0x0001 results in a clock rate of ½(system clock); a COUNTn of 0x0002
or 0x0003 results in a clock rate of ¼(system clock).
The baud rate counter can also be configured as an integer divide by enabling INTDIV in the
EPICFG register. When enabled, COUNTn of 0x0000 or 0x0001 results in a clock rate equal to
system clock. COUNTn of 0x0002 results in a clock rate of 1/2 (system clock). COUNTn of 0x0003
results in a clock rate of 1/3 (system clock).
EPI Main Baud Rate (EPIBAUD)
Base 0x400D.0000
Offset 0x004
Type RW, reset 0x0000.0000
16171819202122232425262728293031
COUNT1
RWRWRWRWRWRWRWRWRWRWRWRWRWRWRWRWType
0000000000000000Reset
0123456789101112131415
COUNT0
RWRWRWRWRWRWRWRWRWRWRWRWRWRWRWRWType
0000000000000000Reset
859June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller
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