MC68HC11EA9 Datasheet, PDF (26/58 Pages) Motorola, Inc – 8 BIT HCMOS SINGLE CHIP MICROCONTOROLLER WITH A/D CONVERTER

Freescale Semiconductor, Inc.
6 Parallel Input/Output
The MC68HC(7)11EA9 has up to 36 input/output lines, depending on the operating mode. Table 10
shows the configuration and features of each port.
Port
A
B
C
D
E
—
—
Input
Pins
—
—
—
—
8
1
1
Table 10 I/O Port Configuration
Output
Pins
—
—
—
—
—
—
—
Bidirectional
Pins
8
8
8
2
—
—
—
Shared Functions
Timer
High Order Address
Multiplexed Low Order Address/Data
SCI/PLL Test
A/D Converter
XPIN (XIRQ pin configured for data input)
IPIN (IRQ pin configured for data input)
Simple and full handshake input and output functions are available on ports B and C lines in single-chip
mode. The following is a description of the handshake functions.
In simple strobed mode, port B is a strobed output port and port C is a latching input port. The two ac-
tivities are available simultaneously.
The STRB output is pulsed for two E-clock periods each time there is a write to the PORTB register.
The INVB bit in the PIOC register controls the polarity of STRB pulses. Port C levels are latched into
the alternate port C latch (PORTCL) register on each assertion of the STRA input. STRA edge select,
flag, and interrupt enable bits are located in the PIOC register. Any or all of the port C lines can still be
used as general-purpose I/O while in strobed input mode.
Full handshake modes involve port C pins and the STRA and STRB lines. Input and output handshake
modes are supported, and output handshake mode has a three-stated variation. STRA is an edge de-
tecting input, and STRB is a handshake output. Control and enable bits are located in the PIOC register.
In full input handshake mode, the MCU uses STRB as a ready line to an external system. Port C logic
levels are latched into PORTCL when the STRA line is asserted by the external system. The MCU then
negates STRB. The MCU reasserts STRB after the PORTCL register is read. A mix of latched inputs,
static inputs, and static outputs is allowed on port C, differentiated by the data direction bits and use of
the PORTC and PORTCL registers.
In full output handshake mode, the MCU writes data to PORTCL which, in turn, asserts the STRB output
to indicate that data is ready. The external system reads port C and asserts the STRA input to acknowl-
edge that data has been received.
In the three-state variation of output handshake mode, lines intended as three-state handshake outputs
are configured as inputs by clearing the corresponding DDRC bits. The MCU writes data to PORTCL
and asserts STRB. The external system responds by activating the STRA input, which forces the MCU
to drive the data in PORTCL out on all of the port C lines. The mode variation does not allow part of port
C to be used for static inputs while other port C pins are being used for handshake outputs. Refer to
PIOC register description for further information.
MC68HC11EA9
26
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