
Parallel Input/Output (I/O) Ports
Data Sheet
M68HC11E Family — Rev. 5
114
Parallel Input/Output (I/O) Ports
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MOTOROLA
Full handshake modes use port C pins and the STRA and STRB lines. Input and 
output handshake modes are supported, and output handshake mode has a 
3-stated variation. STRA is an edge-detecting input and STRB is a handshake 
output. Control and enable bits are located in the PIOC register. 
In full input handshake mode, the MCU asserts STRB to signal an external system 
that it is ready to latch data. 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. In this mode, 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 data and asserts the STRA input to acknowledge that data has been 
received. 
In the 3-state variation of output handshake mode, lines intended as 3-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 
PORTC out on all of the port C lines. After the trailing edge of the active signal on 
STRA, the MCU negates the STRB signal. The 3-state 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 the 
6.8 Parallel I/O Control Register
 for 
further information. 
6.8  Parallel I/O Control Register 
The parallel handshake functions are available only in the single-chip operating 
mode. PIOC is a read/write register except for bit 7, which is read only. 
Table 6-2
shows a summary of handshake operations. 
Table 6-2. Parallel I/O Control
STAF 
Clearing 
Sequence
HNDS
OIN
PLS
EGA
Port B
Port C
Simple 
strobed 
mode
Read 
PIOC with 
STAF = 1 
then read 
PORTCL
0
X
X
Inputs latched into 
PORTCL on any 
active edge on 
STRA
STRB pulses 
on writes 
to PORTB
Full-input 
hand-
shake 
mode
Read 
PIOC with 
STAF = 1 
then read 
PORTCL
1
0
0 = STRB 
active level 
1 = STRB 
active pulse
Inputs latched into 
PORTCL on any 
active edge on 
STRA
Normal output 
port, unaffected 
in handshake 
modes
1
0
0
1
F
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n
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