Register Descriptions
1267
SPRUHE8E – October 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
External Peripheral Interface (EPI)
17.11.3 EPI Main Baud Rate (EPIBAUD2) Register, offset 0x008
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. This register must be programmed
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 and COUNT1 are used in quad chip select mode when
different baud rates are selected, See
and
. If different baud rates are
used, COUNT0 is associated with the address range specified by CS2 and COUNT1 is associated with
the address range specified by CS3.
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,
EPIClockFreq = SystemClockFreq
otherwise
EPIClockFreq
=
SystemClockFreq
/ ([Countn / 2] + 1) × 2
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 1/2 (system clock); a COUNTn of 0x0002
or 0x0003 results in a clock rate of 1/4 (system clock)
Figure 17-30. EPI Main Baud Rate (EPIBAUD2) Register [offset 0x008]
31
16 15
0
COUNT1
COUNT0
R/W-0
R/W-0
LEGEND: R/W = Read/Write; R = Read only; -
n
= value after reset
Table 17-16. EPI Main Baud Rate (EPIBAUD2) Register Field Descriptions
Bit
Field
Value
Description
31-16
COUNT1
CS3 Baud Rate Counter 1
This bit field contains a counter used to divide the system clock by the count.
0
A count of 0 means the system clock is used as is.
1
This bit field is only valid when quad chip selects are enabled by setting the CSCFGEXT bit to 1
and the CSCFG field to 0x1 or 0x2. In addition, the CSBAUD bit must be set in the EPIHBnCFG2
register.
15-0
COUNT0
CS2 Baud Rate Counter 0
This bit field contains a counter used to divide the system clock by the count.
0
A count of 0 means the system clock is used as is.
1
This bit field is only valid when quad chip selects are enabled by setting the CSCFGEXT to 1 and
the CSCFG field to 0x1 or 0x2. In addition, the CSBAUD bit must be set in the EPIHBnCFG2
register.