Technical information

AN2317/D
14 Low-Cost Programming and Debugging Options for M68HC08 MCUs
User Monitor Mode
Implementation
The evaluation board shown in Figure 8 was built for the introduction of the
8-pin MC68HC908QT4 MCU. This board has a preprogrammed
M68HC908QT4 on it that jumps to the monitor mode firmware when the PTA2
pin is held low during power-up. This MCU has so few pins that a full MON08
interface takes just about every pin on the chip. The “user monitor” is a program
residing in FLASH that allows the MCU to enter the monitor mode without V
TST
,
an oscillator, or the mode select pins. That is, the MON08 connector is not
needed at all! The user monitor program is fully described in the application
note entitled User Mode Monitor Access for MC68HC908QY/QT Series MCUs,
Motorola document order number AN2305/D.
Figure 8. Low-Cost Evaluation Board Schematic
5
9
4
8
3
7
2
6
1
DB9
V
DD
PTA5/AD3
PTA4
PTA3
V
SS
PTA0
PTA1/TCH1
PTA2/IRQ
1
2
3
4
VR1
20 kΩ
V
DD
C7
SW1
8
7
6
5
LED1
V
DD
R4
330 Ω
R3
1 kΩ
R2
10 kΩ
V
DD
D1
1N4148
MC68HC908QT4 MAX232
C1+
V+
C1–
C2+
V
CC
GND
T1
Out
R1
In
C2–
V–
T2
Out
R2
In
R1
Out
T1
In
T2
In
R2
Out
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
Tx
Rx
DTR
GND
V
DD
+
C2
1 µF
+
C6
1 µF
+
C5
1 µF
+
C4
1 µF
+
C3
1 µF
V
DD
+
9 V
BATT
C1
0.33 µF
IN OUT
GND
MC7805CT
0.1 µF
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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