TINY-2/MICRO-2 Technical Ref., 2. Ed 1989
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RS-232C Handshaking Protocol
The CTS and RTS lines of the TINY-2/MICRO-2 serial port (labeled P4 on the circuit board and RS-
232C on the rear panel) are used by the TINY-2/MICRO-2 firmware for hardware "handshaking" to
control the flow of data between the computer and the packet controller.
The TINY-2/MICRO-2 always asserts (makes true) Data Set Ready (DSR) on P4 pin 6 via a pullup
resistor. Thus, whenever the TINY-2/MICRO-2 is powered up, it signals to the computer connected
to P4 that the packet controller is "on line".
The computer terminal indicates it is ready to receive data from the TINY-2/MICRO-2 by asserting
its Request To Send (RTS) Signal on P4 pin 4. The packet controller will send data when RTS is as-
serted (if there is data to be sent). If the computer is not ready to receive data, it negates (make
false) RTS to the TINY-2/MICRO-2. Thus, data flow from the packet controller to the computer is
controlled by the use of the RTS line.
The packet controller asserts its Clear To Send (CTS) Output, P4 pin 5, whenever it is ready to re-
ceive data from the computer, if the TINY-2/MICRO-2's buffers fill, it will negate CTS, signaling the
computer to stop sending data. The packet controller will assert CTS when it is again ready to re-
ceive data from the computer. Thus, data flow from the computer to the packet controller is regu-
lated by the use of the CTS line. The CTS line is always toggled, even if "software flow control" is
enabled in this direction.
If "software flow control" is preferred, or if the computer terminal serial I/O port does not imple-
ment CTS/RTS and DTR/DSR handshaking, then a three wire cable should be used. If these RS-
232 control lines are not connected they will be pulled up (and thus asserted) by resistors at the
TINY-2/MICRO-2 end and proper operation will result. However, a non-standard serial port may
use some pins for other purposes, such as supplying power to a peripheral device, so be sure that
the system either implements the CTS, RTS and DSR handshake or has no connections to these
pins of P4 whatsoever. Note that reference to RS-232C "compatibility" or the presence of a DB-25
type connector does not guarantee that you have a standard RS-232C serial port!
The PacComm TINY-2/MICRO-2 packet controller supports asynchronous computer terminal baud
rates of 300, 1200, 2400, 4800, 9600 and 19,200. The port supports standard parity options as
well as 7- or 8-bit character lengths. Factory settings are 1200 bauds, eight bit wordlength, no par-
ity and one stop bit. (UK = 1200, 7, E, 1)
If you want to interface the TINY-2/MICRO-2 with a device configured as DCE, such as a tele-
phone modem or another packet controller, a so-called "null modem" cable may be constructed to
interchange the data and handshake signals.
