© Microhard Systems Inc.
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3.0 Hardware Description
RxD
TxD
RING
…
…
Data byte 1
Data byte 2
Data byte 3
Data byte N
Byte 1
D0 D1 D7
Byte 2
D0 D1 D7
Byte 3
D0 D1 D7
Byte N
D0 D1 D7
…
…
USR_SCK
CTS
Don’t care
Up to 300 µs
Drawing 3-7: Data transfer from user device to modem (Long Packet)
3.2.2 Data Transfer — User Device to modem
When the user has data to send to a modem it must have sensed the falling edge of the CTS line,
and the CTS line must currently be low. At this point the modem is configured in receive mode and
waits for the user to start the clock signal and begin data transfer from the user device to the Modem.
The modem will set the CTS signal high up to 300µs after the start of data transmission.
User’s device must supply the clock signal (USR_SCK) to the modem, the bit transition should be
done on the falling edge of clock and modem latched data on rising edge of clock. The size of data
packet must not exceed 1558 bytes. User’s device can start sending the next data packet only when
the falling edge of CTS is detected and CTS is low.
TxD
…
Data byte 1
Byte 1
D0 D1 D7
USR_SCK
CTS
Drawing 3-8: Data transfer from user device to modem (1 Byte Packet)
