mc9s12e256 Freescale Semiconductor, Inc, mc9s12e256 Datasheet - Page 547

• Manufacturer Part Number: mc9s12e256
• Description: Hcs12 Microcontrollers 16-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

19.3.2.4
Read: Anytime
Write: As stated in each bit description
This register initializes miscellaneous control functions.
Freescale Semiconductor
1. The reset state of this bit is determined at the chip integration level.
EXSTR[1:0]
Reset: Special Test
ROMHM
ROMON
Reset: Expanded
Reset: Peripheral
Field
3:2
or Single Chip
1
0
or Emulation
External Access Stretch Bits 1 and 0
Write: once in normal and emulation modes and anytime in special modes
This two-bit field determines the amount of clock stretch on accesses to the external address space as shown in
Table
FLASH EEPROM or ROM Only in Second Half of Memory Map
Write: once in normal and emulation modes and anytime in special modes
0 The fixed page(s) of FLASH EEPROM or ROM in the lower half of the memory map can be accessed.
1 Disables direct access to the FLASH EEPROM or ROM in the lower half of the memory map. These physical
ROMON — Enable FLASH EEPROM or ROM
Write: once in normal and emulation modes and anytime in special modes
This bit is used to enable the FLASH EEPROM or ROM memory in the memory map.
0 Disables the FLASH EEPROM or ROM from the memory map.
1 Enables the FLASH EEPROM or ROM in the memory map.
Miscellaneous System Control Register (MISC)
locations of the FLASH EEPROM or ROM remain accessible through the program page window.
Writes to this register take one cycle to go into effect.
W
R
19-6. In single chip and peripheral modes these bits have no meaning or effect.
Stretch Bit EXSTR1
0
0
0
0
7
Figure 19-6. Miscellaneous System Control Register (MISC)
0
0
1
1
= Unimplemented or Reserved
Table 19-6. External Stretch Bit Definition
0
0
0
0
6
Table 19-5. MISC Field Descriptions
MC9S12E256 Data Sheet, Rev. 1.08
Stretch Bit EXSTR0
0
0
0
0
5
0
1
0
1
NOTE
Description
0
0
0
0
4
Number of E Clocks Stretched
EXSTR1
1
1
1
3
Chapter 19 Module Mapping Control (MMCV4)
0
1
2
3
EXSTR0
2
1
1
1
ROMHM
0
0
0
1
ROMON
—
0
1
0
1
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