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DEMO908QB8

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21
DEMO908QB8 MARCH 18, 2005
13
RESET SWITCH
The RESET switch provides a method to apply an asynchronous RESET to the MCU. The
RESET switch is connected directly to the RST* input on the MCU. Pressing the RESET
switch applies a low voltage level to the RST* input. A pull-up bias resistor on the RST* input
allows normal MCU operation. Shunt capacitance ensures an adequate input pulse width.
LOW VOLTAGE INHIBIT
The MC68HC908QB8 utilizes an internal Low Voltage Inhibit (LVI) protect against under-
voltage conditions. The LVI is enabled for 2.2Voperation out of RESET. The user must con-
figure the LVI for +5V operation is this feature is to be used. Consult the MC68HC908QB8
reference manual for details on configuring LVI operation.
TIMING
The DEMO908QB8 has 2 timing sources available to the user. The internal oscillator operates
at one of three, user selectable internal timing frequencies: 12.8 MHz, 8.0 MHz, or 4.0 MHz.
Out of reset, the internal oscillator is set to 4MHz with a frequency tolerance of less than 25%.
An 8-bit register allows trimming the internal oscillator to a tolerance of 0.4%. Refer to the
MC68HC908QB8 data sheet for details on internal oscillator operation.
An alternate clock oscillator has also been provided. An option jumper enables/disables the
use of the external oscillator to the MCU. The external oscillator is connected to PTA5 on the
MCU. The user must configure the MCU for operation with the external clock source. Refer to
the MC68HC908QB8 data sheet for details.
The alternate clock oscillator input is not installed in default configuration. Refer to the board
schematic to populate this option and associated circuitry.
Figure 6: J6 Option Header
ON
Enables Clock Oscillator Input to MCU
1 2OFF
Disables Clock Oscillator Input to MCU
NOTE: This option header is not installed in default configuration.
COMMUNICATIONS
The DEMO908QB8 board provides a single Enhanced Serial Communications Interface
(ESCI) port. The ESCI port may be configured for RS-232 serial communications or for LIN
serial communications. RS-232 communications are supported through a DB9 connector. LIN
communications are supported through a pair of 4-pin Molex connectors.
The COM_SEL option header selects the communications protocol applied by the user.
DEMO908QB8 MARCH 18, 2005
14
RS-232
An RS-232 translator provides RS-232 to TTL/CMOS logic level translation on the COM con-
nector. The COM connector is a 9-pin Dsub, right-angle connector. A ferrite bead on shield
ground provides conducted immunity protection. Communication signals TXD and RXD are
routed from the transceiver to the MCU. Hardware flow control signals RTS and CTS are
available on the logic side of U3. These signals are routed to vias located near the transceiver
(U3). RTS has been biased properly to support 2-wire RS-232 communications.
Communications signals TXD and RXD also connect to general purpose Port B signals. The
RS-232 translator should be disconnected at the COM_SEL option header if the general-
purpose I/O signals are used.
Figure 7: COM Connections
MCU Port COM Signal I/O PORT
CONNECTOR
PTB5/TXD TXD OUT J1-5
PTB4/RXD RXD IN J1-7
COM Connector
A standard 9-pin Dsub connector provides external connections for the ESCI port. The Dsub
shell is connected to board ground through a ferrite bead. The ferrite bead provides noise
isolation on the RS-232 connection. The figure below details the DB9 connector.
Figure 8: COM Connector
1
6
TXD
2
7
RTS
RXD
3
8
CTS
4
9
NC
GND
5
Female DB9 connector that interfaces to the HC08 internal SCI1 serial
port via the U2 RS232 transceiver. It provides simple 2 wire asynchro-
nous serial communications without flow control. Flow control is provided
at test points on the board.
Pins 1, 4, and 6 are connected together.
COM_SEL
The communications mode is determined by the COM_SEL jumper. This 3-pin jumper allows
the user to select between RS-232 communications and LIN communications. The figure be-
low shows the different configurations.
DEMO908QB8 MARCH 18, 2005
15
Figure 9: COM_SEL Option Header
COM_SEL
5 3 1
6 4 2
Select LIN communications
LIN
COM
COM_SEL
5 3 1
6 4 2
Select COM communications
LIN
COM
LIN Communications
The DEMO908QB8 applies the MC33661D Local Interconnect Interface (LIN) physical layer
(PHY) for use in developing automotive control applications. The MC33661D PHY support LIN
bus functionality for input voltages between +6V and +18V. Only power applied to the PWR
connector will enable the LIN bus. The COM_SEL option header selects the LIN interface (see
COM_SEL above). Two, 4-pin, Molex connectors provide off-board connectivity. The figure
below shows the pin-out of the LIN connector looking into the connector.
Figure 10: LIN Connector
LIN I/O
4 3
V
SUP
GND
2 1
GND
REF: Mating Connector, Molex P/N,
39-01-2040, Housing
39-00-0039, Socket
NOTE: Board must be powered from the PWR connector with V
IN
+6V and 18V.
USER OPTIONS
The DEMO908QB8 includes various User input and output devices to aid application develop-
ment. User I/O devices include 2 momentary pushbutton switches, 2 green LEDs, 1 potenti-
ometer, and 1 photocell. Each device may be enabled or disabled individually by the USER
option header. A table marked on the board indicates which USER option connects to each
I/O device.
Pushbutton Switches
Two push button switches provide momentary active low input for user applications. Switches
SW1 and SW2 are enabled to the HC08 I/O ports by the USER option bank. SW1 and SW2
provide input to HC08 I/O ports PTA4 and PTA5 respectively. The table below details the user
jumper settings.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21

DEMO908QB8

Mfr. #:
Buy DEMO908QB8
Manufacturer:
NXP / Freescale
Description:
Development Boards & Kits - S08 / S12 HC908QB8 DEM BOARD
Lifecycle:
New from this manufacturer.
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