Download TC1775 User`s Manual System Units

TC1775
System Units
External Bus Unit
BOOTCFG
EBU External Boot Memory Configuration Word
Boot Memory Offset Address + 04H
15
14
13
CFG CMULT
32 CMULTR
12
11
BCGEN
10
9
8
7
6
WAITRDC WAI
T CFG SET
[4:3]
INV 16 UP
5
4
WAIT
3
2
1
WAITRDC
[6:5]
0
AGEN
Note: The gray shaded bit fields are only evaluated by the EBU if bit field BOOTCFG.7
(bit CFG16) is set.
Bit fields AGEN, WAITRDC, WAIT, SETUP, WAITINV, BCGEN, CMULTR, and CMULT
have exactly the same meaning as the respective fields in register EBU_BUSCON0. At
the end of the boot access, the EBU_BUSCON0 fields will be overwritten with the
respective values read from the configuration word BOOTCFG.
Note: During boot, the upper two bits (8-bit boot memory data width selected) or the
upper four bits (16/32-bit boot memory data width selected) of bit field WAITRDC
of CS0 will be loaded.
Note: During boot, bit fields CMULTR and CMULT are loaded with the same value
defined by the external boot memory configuration word BOOTCFG[14:13] when
16/32-bit boot memory data width is selected.
Bits CFG16 and CFG32 determine the data width of the boot memory according to the
Table 12-16:
Table 12-16 Boot Memory Data Width Encoding
CFG32
CFG16
Boot Memory Data Width
don’t care
0
00B: 8-bit
0
1
01B: 16-bit
1
1
10B: 32-bit
If the data width of the boot memory is 8 bits, bit CFG16 is set to 0, and the EBU will only
read and evaluate bits 7..0 of the boot word BOOTCFG. The parameters for BCGEN,
CMULTR and CMULT then must be set by software. It is advisable to perform this early
in the initialization code of the application because the EBU uses the default number of
waitstates to read the boot memory.
If the data width of the boot memory is 16 bits or 32 bits, bit CFG16 in the boot word is
set to 1, and the EBU reads and evaluates bits 15..0 of the boot word BOOTCFG. Bit
CFG32 is set to 0 in case of a 16-bit boot memory, and set to 1 if the data width of the
boot memory is 32 bits. The EBU will update bit field EBU_BUSCON0.PORTW
according to the data width of the boot memory.
User’s Manual
12-43
V2.0, 2001-02