Zilog Z16C35 - Manual (Page 278)

Application Note
Boost Your System Performance Using The Zilog ESCC
™
13-11
1
DMA Request on Transmit Deactivation
Timing /DTR//REQ.
Timing implementation in the ESCC has been improved to
make it more compatible with the DMA cycle timing
(Reference Tech Manual, Section 2.5.2; DMA Request on
Transmit).
Transmission of Back-To-Back Frames with
a Shared Flag.
The ESCC provides facilities to allow transmission of
back-to-back frames with a shared flag between frames
(Figure 13).
In the ESCC, if the Automatic End Of Message (EOM)
Reset feature is enabled (WR7' D1=1), data for a second
frame is written to the transmit FIFO when Tx
Underrun/EOM interrupt has occurred. This allows
application software sufficient time to write the data to the
transmit FIFO while allowing the current frame to be
concluded with CRC and flag.
In the SCC, Transmission of Back-to-Back Frames is more
difficult because (Figure 14):
1. Data cannot be written to the transmitter at EOF until
a Transmit Buffer Empty interrupt is generated after
CRC has completed transmission.
2. Automatic EOM Reset is not available in the SCC.
Application software has to issue the “Reset
Tx/Underrun EOM” command manually. The software
overhead limits the next frame data to deliver
immediately after the preceding frame has been
concluded with CRC and Flag.
Figure 12. Receive Interrupt Mechanism 2
Receive Interrupt on 1st
Special Conditions or In
Receive Characters or Spec
Receive Char
Available In
Specia
Conditi
Interr
Data
FIFO
Locke
Erro
Rese
Data
FIFO
Unloc
CRC err
Overrr
Error
Pari
Erro
End o
Frame
Receiv
Char.
Availa
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