mc9s12e256 Freescale Semiconductor, Inc, mc9s12e256 Datasheet - Page 524

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

Chapter 18 Multiplexed External Bus Interface (MEBIV3)
524
NOACCE
NECLK
LSTRE
PIPOE
RDWE
Field
7
5
4
3
2
CPU No Access Output Enable
Normal: write once
Emulation: write never
Special: write anytime
1 The associated pin (port E, bit 7) is general-purpose I/O.
0 The associated pin (port E, bit 7) is output and indicates whether the cycle is a CPU free cycle.
This bit has no effect in single-chip or special peripheral modes.
Pipe Status Signal Output Enable
Normal: write once
Emulation: write never
Special: write anytime.
0 The associated pins (port E, bits 6:5) are general-purpose I/O.
1 The associated pins (port E, bits 6:5) are outputs and indicate the state of the instruction queue
This bit has no effect in single-chip or special peripheral modes.
No External E Clock
Normal and special: write anytime
Emulation: write never
0 The associated pin (port E, bit 4) is the external E clock pin. External E clock is free-running if ESTR = 0
1 The associated pin (port E, bit 4) is a general-purpose I/O pin.
External E clock is available as an output in all modes.
Low Strobe (LSTRB) Enable
Normal: write once
Emulation: write never
Special: write anytime.
0 The associated pin (port E, bit 3) is a general-purpose I/O pin.
1 The associated pin (port E, bit 3) is configured as the LSTRB bus control output. If BDM tagging is enabled,
This bit has no effect in single-chip, peripheral, or normal expanded narrow modes.
Note: LSTRB is used during external writes. After reset in normal expanded mode, LSTRB is disabled to provide
Read/Write Enable
Normal: write once
Emulation: write never
Special: write anytime
0 The associated pin (port E, bit 2) is a general-purpose I/O pin.
1 The associated pin (port E, bit 2) is configured as the R/W pin
This bit has no effect in single-chip or special peripheral modes.
Note: R/W is used for external writes. After reset in normal expanded mode, R/W is disabled to provide an extra
TAGLO is multiplexed in on the rising edge of ECLK and LSTRB is driven out on the falling edge of ECLK.
an extra I/O pin. If LSTRB is needed, it should be enabled before any external writes. External reads do
not normally need LSTRB because all 16 data bits can be driven even if the system only needs 8 bits of
data.
I/O pin. If R/W is needed it should be enabled before any external writes.
Table 18-6. PEAR Field Descriptions
MC9S12E256 Data Sheet, Rev. 1.08
Description
Freescale Semiconductor