Zhou Hongliang

Why the voltage of MISO between MC9S12DP256B and MC68CH908AZ60 is 2.5V?

Discussion created by Zhou Hongliang on Dec 6, 2006
Latest reply on Dec 8, 2006 by John Hassler
Hi.
I have designed an ECU with MC9S12DP256B and MC68HC908AZ60 (maybe I should use
MC68HC908AZ60A). The two MCUs communicate via SPI.
The detail of the connection and voltage of the MISO could be seen in the attachment.
DP256B is in MASTER mode, while AZ60 is in SLAVE mode.
When the program runs, DP256B could transmit data to AZ60, but the received data of DP256B is wrong.
So I check the voltage of MISO and I fould that when transmitting data, the voltage of MISO is normal, that is 0V in low condition and 5V in high condition. But in idle condition, when the CLK is hold high, the vlotage of MISO is 2.5V.
Why?
What should I do to keep the communication between DP256B and AZ60 correctly?
How could I configure CPOL and CPOA or other register?
Thank you.
 
Message Edited by t.dowe on 2009-10-21 12:17 AM

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