Operating Modes and On-Chip Memory
M68HC11E Family Data Sheet, Rev. 5.1
42
Freescale Semiconductor
IRV(NE) — Internal Read Visibility (Not E) Bit
IRVNE can be written once in any mode. In expanded modes, IRVNE determines whether IRV is on
or off. In special test mode, IRVNE is reset to 1. In all other modes, IRVNE is reset to 0. For the
MC68HC811E2, this bit is IRV and only controls the internal read visibility function.
0 = No internal read visibility on external bus
1 = Data from internal reads is driven out the external data bus.
In single-chip modes this bit determines whether the E clock drives out from the chip. For the
MC68HC811E2, this bit has no meaning or effect in single-chip and bootstrap modes.
0 = E is driven out from the chip.
1 = E pin is driven low. Refer to the following table.
PSEL[3:0] — Priority Select Bits
2.3.3 System Initialization
Registers and bits that control initialization and the basic operation of the MCU are protected against
writes except under special circumstances.
Table 2-2 lists registers that can be written only once after
reset or that must be written within the first 64 cycles after reset.
0
Bootstrap
1
0
1
Special test
1
Mode
IRVNE Out
of Reset
E Clock Out
of Reset
IRV Out
of Reset
IRVNE
Affects Only
IRVNE Can
Be Written
Single chip
0
On
Off
E
Once
Expanded
0
On
Off
IRV
Once
Bootstrap
0
On
Off
E
Once
Special test
1
On
IRV
Once
Table 2-2. Write Access Limited Registers
Operating
Mode
Register
Address
Register Name
Must be Written
in First 64 Cycles
Write
Anytime
SMOD = 0
$x024
Timer interrupt mask 2 (TMSK2)
Bits [1:0], once only
Bits [7:2]
$x035
Block protect register (BPROT)
Clear bits, once only
Set bits only
$x039
System configuration options (OPTION)
Bits [5:4], bits [2:0], once only
Bits [7:6], bit 3
$x03C
Highest priority I-bit interrupt
and miscellaneous (HPRIO)
See HPRIO description
$x03D
RAM and I/O map register (INIT)
Yes, once only
—
SMOD = 1
$x024
Timer interrupt mask 2 (TMSK2)
—
All, set or clear
$x035
Block protect register (BPROT)
—
All, set or clear
$x039
System configuration options (OPTION)
—
All, set or clear
$x03C
Highest priority I-bit interrupt and
miscellaneous (HPRIO)
See HPRIO description
$x03D
RAM and I/O map register (INIT)
—
All, set or clear