Zilog Z16C35 - Manual (Page 275)

Application Note
Boost Your System Performance Using The Zilog ESCC ™
13-8
AUTOMATIC OPENING FLAG TRANSMISSION
When Auto Tx Flag (WR7', D0) is enabled, the ESCC
automatically transmits a SDLC opening flag before
transmitting data. This removes:
1. Requirements to reset the mark idle bit (WR10 D3)
before writing data to the transmitter, or;
2. Waiting for eight bit times to load the opening flag.
TxD Forced High In SDLC With NRZI Encod-
ing When Marking Idle After End Of Frame
When the ESCC is programmed for SDLC mode with NRZI
encoding and mark idle (WR10 D6=0,D5=1,D3=1), TxD is
automatically forced high when the transmitter goes to the
mark idle state at EOF or when Abort is detected. This
feature is used in combination with the automatic SDLC
opening flag transmission to format the data packets
between successive frames properly without any
requirement in software intervention.
Status FIFO Enhancement
ESCC SDLC Frame Status FIFO implementation has
been improved to maximize ESCC ability to interface with
a DMA-driven system (Technical Manual, 4.4.3). The
Status FIFO and its relationship with RR1, RR6 and RR7
is shown in Figure 8.
Other special conditions (e.g., Overrun) generates special
receive conditions and lock the Receiver FIFO (Figures 9
and 10).
Figure 8. Status FIFO
Loaded If
Status FIFO
Is Enabled
Status
FIFO
RR7 RR6
Byte Count
Residue
Code
RX
Overrun
Error
CRC/Framing
Error
RR1
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