Zilog Z16C30 User Manual

Page 108

5-41

Z16C30 USC

SER

ANUAL

ILOG

UM97USC0100

RTCmd

Reset

RTMode

Chan

Load

B//W

RegAddr

U//L

Figure 5-19. The Channel Command/Address Register (CCAR)

A description of each command follows, in alphabetical
order. Some of them include references to other chapters
or sections, which provide more information that’s impor-
tant to fully understanding the command.

Clear EOF/EOM

(TCmd:=1110): this command condi-

tions a channel so that it doesn’t mark the next character
that software or an external Transmit DMA controller writes
to the Transmit Data Register as End of Frame/End of
Message. Since a channel assumes this state after each
write to the TDR, and after a hardware or programmed
Reset, software will need this command only if it “changes
its mind” about where the frame ends, between issuing a
Set EOF/EOM command and writing the TDR.

Clear Rx or Tx CRC Generator

(RCmd or TCmd:= 0010):

these commands force the Receive or Transmit CRC
Generator to all zeroes or all ones, depending on the
RxCRCStart bit in the Receive Mode Register (RMR10) or
the TxCRCStart bit in the Transmit Mode Register (TMR10).
Software will seldom need these commands because the
Receiver and Transmitter automatically clear their associ-
ated CRC generators at the start of each frame.

Disable DLE Insertion

(TCmd:=1101): this command

applies only to Transparent Bisync mode. It conditions a

channel so that it doesn’t check subsequent characters
written to the Transmit Data Register (TDR) for DLE char-
acters, and so that it doesn’t add any DLE characters to the
transmitted data stream. Software should use this com-
mand before writing a two-character control sequence
that starts with DLE to the TDR. DLE insertion remains
disabled until software issues an Enable DLE Insertion
command or until a hardware or software Reset. Each
channel queues the state that’s affected by this and the
following command through its TxFIFO with each charac-
ter, so that software can change the state as needed.

Enable DLE Insertion

(TCmd:=1100): this command ap-

plies only to Transparent Bisync mode. It conditions a
channel so that it checks subsequent characters written to
the Transmit Data Register (TDR) for DLE characters, and
adds another DLE for each DLE written to the TDR. Soft-
ware should use this command before writing normal data
to the TDR. DLE insertion remains enabled until software
issues a Disable DLE Insertion command. Each channel
queues the state that’s affected by this and the preceding
command through its TxFIFO with each character, so that
software can change the state as needed.

UM009402-0201