RCVDL56DPFL/SP, RCV56DPFL/SP, and RCV336DPFL/SP Designer’s Guide
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After the FCS transmission (immediately following bit x0), one flag is sent to signify the end of the current frame and the
beginning of the next frame. After the final zero in a flag is transmitted, the MDP looks to see if the host has loaded new data
into TBUFFER. If no new data is loaded before this time, another flag is sent. Therefore, if more than one flag between
frames is desired, the host must wait N-1 multiples of eight bit times after FLAGS is set by the MDP to load new data into
TBUFFER, where N is the number of flags. The host then has seven bit times in which to load new data and thus prevent
another flag from being sent. For example, if three flags are desired between frames, the host must wait at least 16 bit times
and not more than 23 bit times after FLAGS is set by the MDP.
Abort/Idle Sequence Transmission and Reception
The MDP receiver not only continually searches for flags, but also continually searches for an abort/idle sequence. When the
MDP detects this data pattern, it sets the FE bit (0Ah:4). The reception of data following the abort/idle sequence is treated as
invalid data and is not presented to the host. Therefore, to re-establish transmitter and receiver synchronization, the receiver
must see at least one flag. If FE is set, the current received data byte (typically FFh) should be discarded.
5.3 EXAMPLE APPLICATION
Refer to Table 3-1 for a description of the bits associated with the HDLC functions. Figure 5-2 illustrates bit timing.
5.3.1 Transmitter Example (Tx FIFO Disabled)
The steps to perform a typical HDLC transmission with the Transmitter FIFO disabled are (Figure 5-2a):
1. Set the MDP configuration in CONF; reset the ASYN and FIFOEN bits; set the HDLC, TPDM, and RTS bits.
2. The MDP starts transmitting flags immediately and continues with flags until the first byte of data is loaded into
TBUFFER.
3. Wait for TDBE = 1, then place the first byte of data into TBUFFER. The MDP finishes transmitting the current flag
followed by this byte of data.
4. As soon as TDBE is set, load in the next byte of data. This must occur within 2.5 bit times of TDBE being set.
5. After all information but the last byte is given to the MDP, load in the last byte of data in the frame as in step 4.
6. Wait until FLAGS is set to load in the first byte of the next frame. The MDP follows the last byte of the current frame with
the FCS and a flag.
7. Repeat steps 4 through 6 for all frames to be transmitted.
5.3.2 Transmitter Example (Tx FIFO Enabled)
The steps to perform a typical HDLC transmission with the Transmitter FIFO enabled are:
1. Set the MDP configuration in CONF; reset the ASYN bit; set the FIFOEN, HDLC, TPDM, and RTS bits.
2. The MDP starts transmitting flags immediately and continues with flags until the first byte of data is loaded into
TBUFFER.
3. Place the first byte of data into TBUFFER. The MDP finishes transmitting the current flag followed by this byte of data.
4. Continue to load data in TBUFFER until TXFNF = 0 or the last byte of the frame is reached.
5. After all information but the last byte is given to the MDP, set TEOF, then load in the last byte of data in the frame as in
step 4.
6. Reset TEOF to 0.
7. Repeat steps 4 through 6 for all frames to be transmitted.
Summary of Contents for RC336DPFL
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