SystemClockFreq
EPIClockFreq
COUNTn
1
2
2
§
·
ª
º
u
¨
¸
«
»
¬
¼
©
¹
EPIClockFreq
SystemClockFreq
EPI Registers
1125
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
External Peripheral Interface (EPI)
16.5.2 EPIBAUD Register (Offset = 0x4) [reset = 0x0]
EPI Main Baud Rate (EPIBAUD)
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
and
. 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,
(57)
otherwise:
(58)
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).
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).
EPIBAUD is shown in
and described in
.
Return to
Figure 16-31. EPIBAUD Register
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
COUNT1
COUNT0
R/W-0x0
R/W-0x0
Table 16-15. EPIBAUD Register Field Descriptions
Bit
Field
Type
Reset
Description
31-16
COUNT1
R/W
0x0
Baud Rate Counter 1 This bit field is only valid with multiple chip
selects which are enabled when the CSCFG field is 0x2 or 0x3 or
the CSCFGEXT field is set to 1, with CSCFG field as 0x1 or 0x2 and
the CSBAUD bit is set in the EPIHBnCFG2 register.
This bit field contains a counter used to divide the system clock by
the count.
A count of 0 means the system clock is used as is.
15-0
COUNT0
R/W
0x0
Baud Rate Counter 0 This bit field contains a counter used to divide
the system clock by the count.
A count of 0 means the system clock is used as is.