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4.1.2 SW2 Settings
Switch SW2 is used to set the SP-5000 printer’s serial port pinout configuration. The printer can be set to it’s own
configuration or PC/AT pinout.
4.1.3 DB-9 RS-232 Serial Interface
The SP-5000 serial interface incorporates a DB-9 connector whose pinout configuration can be changed via SW2
from the SP-5000 to a PC/AT compatible configuration.
Pin Signal Description
1 GROUND Protective ground
2 TXD Data output from the printer to the host
3 RXD Data input to the printer or display
4 CTS Inhibits TXD line when held at -10v by the host
5 GROUND Signal ground
8 DTR -10v when printer is unable to receive data
There are two conventions used in the RS-232C interface; these are Data Terminal Equipment (DTE) and Data
Communications Equipment (DCE). Examples of DCE are modems, multiplexers, and telephone data line
interfaces. All other equipment which originates or receives data such as terminals (including the SP-5000) or
computers is DTE. The difference between DCE and DTE is that TXD and RXD are reversed, as well as several
control signals.
This allows a piece of DTE to connect directly to a piece of DCE, e.g. a modem to a terminal, with a straight pin for
pin connection in the interconnecting cable. However if two pieces of DTE are to be interconnected it is necessary
to transpose TXD and RXD as well as DTR and CTS in the cable. This type of cable is called a null modem cable
and must be used if the SP-5000 is connected to a host computer’s serial port.
A DB 25S connector is used for the parallel interface. The pin assignments and brief signal descriptions are listed
below.
Pin Signal Description
1 STROBE 1 µsec. pulse to clock data into the printer
2 DATA 0
3 DATA 1
4 DATA 2 Eight data bit input signals to the printer;
5 DATA 3 Signal levels are high for logic 1 and low
6 DATA 4 for a logic 0.
7 DATA 5
8 DATA 6
9 DATA 7
10 ACK 6 µsec pulse from printer when data received
11 BUSY High when printer is unable to receive data
12 PE High when a paper error occurs in printer
13 SELECT High when printer is on line
18-24 GROUND Signal Grounds
4.3 Flow Control
The SP-5000 employs a 31 K byte data buffer (128 and 512 optional) to allow the host computer to rapidly transfer
data. Under some circumstances it may be possible to completely fill the buffer. When the buffer is within 50 bytes
of being full, the SP-5000 signals the host computer to pause until a line of data is printed, or until the buffer is
under the 50 byte limit. The flow control information is sent to the host using hardware and software protocols.
The hardware protocol uses the BUSY line of the parallel interface and the DTR line of the serial interface. These
pins are asserted or negated as necessary to turn off and turn on the flow of data.
XON and XOFF
protocol is offered as an option. The software protocol uses the XON and XOFF ASCII characters
(^Q and ^S) which are sent back to the host to start and stop the data stream. Some host systems may not support
one or both of these protocols. Please contact Telpar for more details regarding the use of this protocol.
4.4 Parallel Port Handshaking Implementation
