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Chapter 5 External Bus Interface (S12XEBIV4)
MC9S12XE-Family Reference Manual Rev. 1.07
Freescale Semiconductor
247
5.3.2.2
External Bus Interface Control Register 1 (EBICTL1)
Read: Anytime. In emulation modes, read operations will return the data from the external bus, in all other
modes the data is read from this register.
Write: Anytime. In emulation modes, write operations will also be directed to the external bus.
This register allows programming of two independent values determining the amount of additional stretch
cycles for external accesses (wait states).
With two bits in S12X_MMC register MMCCTL0 for every individual CSx line one of the two counter
options or the EWAIT input is selected as stretch source. The chip select outputs can also be disabled to
free up the pins for alternative functions (
Table 5-5
). Refer also to S12X_MMC section for register bit
descriptions.
Table 5-5. Chip select function
If EWAIT input usage is selected in MMCCTL0 the minimum number of stretch cycles is 2 for accesses
to the related address range.
If configured respectively, stretch cycles are added as programmed or dependent on EWAIT in normal
expanded mode and emulation expanded mode; function not available in all other operating modes.
Module Base +0x000F (PRR)
7
0
6
5
4
3
0
2
1
0
R
W
EXSTR12
EXSTR11
EXSTR10
EXSTR02
EXSTR01
EXSTR00
Reset
0
1
1
1
0
1
1
1
= Unimplemented or Reserved
Figure 5-4. External Bus Interface Control Register 1 (EBICTL1)
CSxE1
CSxE0
Function
0
0
CSx disabled
0
1
CSx stretched with EXSTR0
1
0
CSx stretched with EXSTR1
1
1
CSx stretched with EWAIT
Table 5-6. EBICTL1 Field Descriptions
Field
Description
6–4
EXSTR1[2:0]
External Access Stretch Option 1 Bits 2, 1, 0
— This three bit field determines the amount of additional clock
stretch cycles on every access to the external address space as shown in
Table 5-7
.
2–0
EXSTR0[2:0]
External Access Stretch Option 0 Bits 2, 1, 0
— This three bit field determines the amount of additional clock
stretch cycles on every access to the external address space as shown in
Table 5-7
.