Samsung ML-920 Service Manual page 158

CIRCUIT DESCRIPTION
nSTROBE
BUSY
PPD( 7: 0)
nAUTOFD
1. The host places data on the data lines and indicates a data cycle by setting nAUTOFD
2. Host asserts nSTROBE low to indicate valid data
3. Peripheral acknowledges host by setting BUSY high
4. Host sets nSTROBE high. This is the edge that should be used to clock the data into the Peripheral
5. Peripheral sets BUSY low to indicate that it is ready for the next byte
6. The cycle repeats, but this time it is a command cycle because nAUTOFD is low
1 2
nACK
nAUTOFD
PPD ( 7: 0)
BUSY
nINI T
PE
1. The host request a reverse channel transfer by setting nINIT low
2. The peripheral signals that it is OK to proceed by setting PE low
3. The peripheral places data on the data lines and indicates a data cycle by setting BUSY high
4. Peripheral asserts nACK low to indicate valid data
5. Host acknow ledges by setting nAUTOFD high
6. Peripheral sets nACK high. This is the edge that should be used to clock the data into the host
7. Host sets nAUTOFD low to indicate that it is ready for the next byte
8. The cycle repeats, but this time it is a command cycle because BUSY is low
Repair Manual
3-28
1 2 3 4 5
BYTE0
DATA BYTE
<ECP Hardware Handshaking Timing (forward) >
3 4 5 6 7
BYTE0
DATA BYTE
<ECP Hardware Handshaking Timing (forward)
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6
BYTE1
COMMAND BYTE
8
BYTE1
COM M AND BYTE
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