exam2 plc

1. EE 134 / EE 101
Spring, 2002
Lecture 19
Exam 2 Solutions

2. Problem 1. Figure 9.16 in text: Input Handshake Timing Diagrams
Peter Spasov
Microcontroller Technology: The
68HC11, Fourth Edition
Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
We are using
Interlocked mode.
STRB active low.
We are not using
pulsed mode here.

3. Another view of Problem 1: FIGURE 9-19 Centronics Parallel Interface Timing Diagram
Peter Spasov
Microcontroller Technology: The
68HC11, Fourth Edition
Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
68HC11
PORTC
STRA
STRB
PORTCL is read
Data is latched into PORTCL
The Centronics
standard is a good
example of input
handshaking, where
the MCU is inside
the printer.
In this problem
we do not have
an ACK signal.

4. * EE101/EE134 Exam 2 (The following is just a sample Main program)
Main
LDX #REGBAS ;set IX for indexed addressing of ports
BSR Init_PortC
New_Data
BSR Input_Data
BSR Display_Bit
BRA New_Data
*********************************************************
*Subroutine: Initialize Port C
*The MCU receives parallel data from the peripheral
*using interlocked handshaking.
* HNDS = 1, all other bits = 0
*Calling register: IX = REGBAS
*Return regiester: none, but ACCA changed
Init_PortC
BCLR DDRC,X $FF ; all inputs (It was OK to not include this)
LDAA #$10
STAA PIOC,X
RTS
*********************************************************
*Subroutine: Wait for data in PORTCL
*Calling register: IX = REGBAS
*Return register: ACCA contains input data
Input_Data
BRCLR PIOC,X $80 Input_Data ; wait for STAF=1
LDAA PORTCL,X ; ACCA = data
RTS

5. Problem 3: FIGURE 9-3 Seven-Segment LED Display Connections
Peter Spasov
Microcontroller Technology: The
68HC11, Fourth Edition
Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
This is the type
of LED display
specified in the
problem.
A low (zero) bit
turns that segment
on.

6. FIGURE 9-4 Seven-Segment Code Examples
Peter Spasov
Microcontroller Technology: The
68HC11, Fourth Edition
Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.

8. *********************************************************
*Subroutine: Display 0 if Z set, 1 if Z clear
*Uses common-anode 7-segment LED display (0=on, 1=off)
*Assume PB0 -> a, PB1 -> b, ..., PB6 -> g, PB7 -> N.C.
*Calling registers: IX = REGBAS, Z bit in CCR
*Return register: none, but ACCA changed
Display_Bit
BNE One ; be sure Z isn't changed before test
Zero
LDAA #$40 ; or $C0
STAA PORTB,X
RTS
One
LDAA #$79 ; or $F9
STAA PORTB,X
RTS

9. Problem 4: FIGURE 9-9 3 x 4 Matrix Keyboard (Telephone Format)
Peter Spasov
Microcontroller Technology: The
68HC11, Fourth Edition
Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.

10. Problem 4: FIGURE 9-10 Parallel I/O with Keyboard. Also connect PC7 high using a pull-up resistor.
Peter Spasov
Microcontroller Technology: The
68HC11, Fourth Edition
Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
With this layout we need to
setup the Port C Data Direction
Register, DDRC, with $0F.

11. Problem 5:
a. Printers
b. Instruments
c. One microsecond (two clock cycles)
d. IRQ
e. 0
f. $D6
g. $1007
h. 0 (or no change)
i. Read, receive, or load
j. Data bus