XR88C681J-F Datasheet, PDF (36/101 Pages) Exar Corporation – Two Full Duplex, Independent Channels

XR88C681
Figure 12 presents the block diagram of the MC68HC11 C.
MODA
MODB
XTAL EXTAL E -IRQ -XIRQ -RESET
Mode Control
Oscillator
Clock Logic
Interrupt
Logic
RAM 256 Bytes
Timer
System
Port A
CPU Core
Bus Expansion
Address
Address/Data
Strobe and Handshake Parallel I/O
8
Port B
Control
Port C
VRH
VRL
SPI
SCI
A/D Converter
Control
Port D
Port E
Figure 12. Block Diagram of the MC68HC11 Microcontroller
The 68HC11 can be configured to operate in a “Single
Chip” Mode or in an “Expanded Multiplexed Bus” mode. If
a device is configured to operate in the “Single Chip”
mode, the entire 64K bytes of Address space is internal to
the C IC. Please note that this does not mean that there
is 64K bytes of memory, or other addressable portions
within the device. A 68HC11 MCU configured for “Single
Chip” mode operation cannot address any components
external to the MCU. Therefore, if a user desired to
interface the DUART to this C, then the C must operate
in the “Expanded-Multiplexed” mode. The MC68HC11 is
configured into the Expanded Multiplexed mode by tying
both the MODA and MODB pin to Vcc, and then resetting
the device.
The MC68HC11 consists of 5 different multi-function
parallel ports. Each of these ports are briefly discussed.
Port A
Port A consists of 3 input pins, 4 output pins and 1
bi-directional pin. This port is used to support the Timer
System. One of the input pins can be used for the Pulse
Rev. 2.11
36