Initialization and Configuration
1098
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
External Peripheral Interface (EPI)
(1)
If the CSBAUD bit in the EPIHBnCFG2 register is clear and multiple
chip selects are enabled, then all chip selects are configured by the
MODE bit field in the EPIHBnCFG register.
Table 16-5. Chip Select Configuration Register
Assignment
Configuration Register
(1)
Corresponding Chip Select
EPIHBnCFG
CS0n
EPIHBnCFG2
CS1n
EPIHBnCFG3
CS2n
EPIHBnCFG4
CS3n
Multiple chip select modes do not allow the intermixing of Host-Bus 8 and Host-Bus16 modes.
When BSEL = 1 in the EPIHB16CFG register, byte select signals are provided, so byte-sized data can be
read and written at any address, however these signals reduce the available address width by 2 pins. The
byte select signals are active Low. BSEL0n corresponds to the LSB of the halfword, and BSEL1n
corresponds to the MSB of the halfword.
When BSEL = 0, byte reads and writes at odd addresses only act on the even byte, and byte writes at
even addresses write invalid values into the odd byte. As a result, accesses should be made as halfwords
(16-bits) or words (32-bits). In C/C++, programmers should use only short int and long int for accesses.
Also, because data accesses in HB16 mode with no byte selects are on 2-byte boundaries, the available
address space is doubled. For example, 28 bits of address accesses 512MB in this mode.
shows the capabilities of the HB8 and HB16 modes as well as the available address bits with the possible
combinations of these bits.
Although the EPI0S31 signal can be configured for the EPI clock signal in Host-Bus mode, it is not
required and should be configured as a GPIO to reduce EMI in the system.
(1)
If byte selects are not used, data accesses are on 2-byte boundaries. As a result, the available address space is doubled.
(2)
Two EPI signals are used for byte selects, reducing the available address space by two bits.
Table 16-6. Capabilities of Host Bus 8 and Host Bus 16 Modes
Host Bus
Type
MODE
CSCFGEXT
CSCFG
Maximum
No. of
External
Devices
BSEL
Byte
Access
Available
Address
Addressable
Memory
HB8
0x0
0
0x0, 0x1
1
N/A
Always
28 bits
256MB
HB8
0x0
0
0x2
2
N/A
Always
27 bits
128MB
HB8
0x0
0
0x3
2
N/A
Always
26 bits
64MB
HB8
0x0
1
0x0
1
N/A
Always
27 bits
128MB
HB8
0x0
1
0x1
4
N/A
Always
27 bits
128MB
HB8
0x0
1
0x2
4
N/A
Always
26 bits
64MB
HB8
0x1
0
0x0, 0x1
1
N/A
Always
20 bits
1MB
HB8
0x1
0
0x2
2
N/A
Always
19 bits
512KB
HB8
0x1
0
0x3
2
N/A
Always
18 bits
256KB
HB8
0x1
1
0x0
1
N/A
Always
19 bits
512KB
HB8
0x1
1
0x1
4
N/A
Always
19 bits
512MB
HB8
0x1
1
0x2
4
N/A
Always
18 bits
256KB
HB8
0x2
0
0x1
1
N/A
Always
20 bits
1MB
HB8
0x3
0
0x1
1
N/A
Always
none
–
HB8
0x3
0
0x3
2
N/A
Always
none
–
HB8
0x3
1
0x0
1
N/A
Always
none
–
HB8
0x3
1
0x1
4
N/A
Always
none
–
HB8
0x3
1
0x2
4
N/A
Always
none
–
HB16
0x0
0
0x0, 0x1
1
0
No
28 bits
(1)
512MB
HB16
0x0
0
0x0, 0x1
1
1
Yes
26 bits
(2)
128MB