Timewave DSP-232, Operating Manual, Page: 60 / 271

Chapter 4 Terminal Interfacing
XOFF n Default: $13 ( CTRL-S )
Host: XF
“n” 0 to $7F (0 to 127 decimal) specifies an ASCII character code.
Use
X OFF
to select the Stop character to be used to stop input from the computer to the DSP.
The Stop character default value is (
CTRL-S ) for computer data transfers.
X ON n Default: $11 ( CTRL-Q )
Host: XN
“n” 0 to $7F (0 to 127 decimal) specifies an ASCII character code.
XON selects the DSP Start character that is sent to the computer to restart input from it to the DSP.
The Start character default value is (
CTRL-Q ) for computer data transfers.
ZFree
Immediate Command
Host: ZF
This command is primarily of interest to HOST mode programmers. ZFREE is an immediate read-only command
that returns the amount of data RAM that is available in the DSP-232. n is the number of free internal memory
blocks. Each memory block holds 28 bytes of data.
Use the ZFREE command to avoid the situation in which a host mode application sends a block of data to be
transmitted, but the controller connot issue a data acknowledgement (5F X X 00) to the host computer rith away
because the TNC is too full. The application should not send data to the controller if it would cause the value of
ZFREE to drop below 64. To avoid the transmission of RNR (device busy) packets, the application should make
sure ZFREE does not drop below 128.
Note that ZFREE is different from the FREE command, which shows the number of message bytes available to the
MailDrop. (ZFREE times 28 is always larger than the value of FREE.)
ZStatus Immediate Command
Host: ZS
This command is primarily of interest to HOST mode programmers. ZSTATUS is an immediate read-only
command. that returns a data byte in hexadecimal indicating the status of the unit as shown in the table below.
BIT
Meaning if 0 Meaning if 1
0 Transmit character RTTY & AMTOR characters
buffer is empty are being transmitted
1
No MailDrop command MailDrop command in progress
in progress
2
No MailDrop messages for The MailDrop contains messages
local sysop for local sysop
September, 05 4-27