MC68HC11PH8 Datasheet, PDF (39/264 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

2.8
MODA and MODB (MODA/LIR and MODB/VSTBY)
During reset, MODA and MODB select one of the four operating modes. Refer to Section 3.
2
After the operating mode has been selected, the LIR pin provides an open-drain output (driven
low) to indicate that execution of an instruction has begun. In order to detect consecutive
instructions in a high-speed application, this signal drives high for a short time to prevent false
triggering. A series of E clock cycles occurs during execution of each instruction. The LIR signal
goes low during the first E clock cycle of each instruction (opcode fetch). This output is provided
for assistance in program debugging and its operation is controlled by the LIRDV bit in the OPT2
register.
The VSTBY pin is used to input RAM stand-by power. The MCU is powered from the VDD pin
unless the difference between the level of VSTBY and VDD is greater than one MOS threshold
(about 0.7 volts). When these voltages differ by more than 0.7 volts, the internal 1024-byte RAM
and part of the reset logic are powered from VSTBY rather than VDD. This allows RAM contents
to be retained without VDD power applied to the MCU. Reset must be driven low before V_DD is
removed and must remain low until V_DD has been restored to a valid level.
V_DD
4.8 V NiCd
(+)
V_DD V_OUT
MAX 690
V_BATT
4.7 kΩ
To MODB/VSTBY
pin of M68HC11
Figure 2-7 RAM stand-by connections
2.9
VRH and VRL
These pins provide the reference voltages for the analog-to-digital converter.
2.10
PG7/R/W
This pin provides two separate functions, depending on the operating mode. In single chip and
bootstrap modes, PG7/R/W acts as input/output port G bit 7. Refer to Section 4 for further information.
In expanded and test modes, PG7/R/W performs the read/write function. PG7/R/W signals the
direction of transfers on the external data bus. A high on this pin indicates that a read cycle is in
progress.
MC68HC11PH8
PIN DESCRIPTIONS
TPG
MOTOROLA
2-13