MC68711E20CFNE3 Datasheet, PDF (30/242 Pages) –

Operating Modes and On-Chip Memory
The address, R/W, and AS signals are active and valid for all bus cycles, including accesses to internal
memory locations. The E clock is used to enable external devices to drive data onto the internal data bus
during the second half of a read bus cycle (E clock high). R/W controls the direction of data transfers. R/W
drives low when data is being written to the internal data bus. R/W will remain low during consecutive data
bus write cycles, such as when a double-byte store occurs.
Refer to Figure 2-1.
NOTE
The write enable signal for an external memory is the NAND of the E clock
and the inverted R/W signal.
PB7
PB6
PB5
PB4
PB3
PB2
PB1
PB0
HC373
PC7
D1 Q1
PC6
D2 Q2
PC5
D3 Q3
PC4
D4 Q4
PC3
D5 Q5
PC2
D6 Q6
PC1
D7 Q7
PC0
D8 Q8
AS
LE OE
R/W
E
MCU
Figure 2-1. Address/Data Demultiplexing
ADDR15
ADDR14
ADDR13
ADDR12
ADDR11
ADDR10
ADDR9
ADDR8
ADDR7
ADDR6
ADDR5
ADDR4
ADDR3
ADDR2
ADDR1
ADDR0
WE
OE
DATA7
DATA6
DATA5
DATA4
DATA3
DATA2
DATA1
DATA0
2.2.3 Test Mode
Test mode, a variation of the expanded mode, is primarily used during Freescale’s internal production
testing; however, it is accessible for programming the configuration (CONFIG) register, programming
calibration data into electrically erasable, programmable read-only memory (EEPROM), and supporting
emulation and debugging during development.
2.2.4 Bootstrap Mode
When the MCU is reset in special bootstrap mode, a small on-chip read-only memory (ROM) is enabled
at address $BF00–$BFFF. The ROM contains a bootloader program and a special set of interrupt and
reset vectors. The MCU fetches the reset vector, then executes the bootloader.
Bootstrap mode is a special variation of the single-chip mode. Bootstrap mode allows special-purpose
programs to be entered into internal random-access memory (RAM). When bootstrap mode is selected
at reset, a small bootstrap ROM becomes present in the memory map. Reset and interrupt vectors are
M68HC11E Family Data Sheet, Rev. 5.1
30
Freescale Semiconductor