Star Micronics NX-1020 Technical Manual page 26

THEORY OF OPERATION
The IC101 is a dual RS-232C driver/receiver which includes a capacitive voltage generator to supply RS-232C voltage
levels from a single 5V supply.
Data from the host computer is sent from RXD via IC101 and is input to the MPU. Serial data input to the MPU is converted
into parallel data, and output to the main logic board. Conversely, parallel data received by the MPU is converted there
into serial data, and output to the TXD terminal via IC101.
The CTS terminal is hardware-connected, not software- connected. (This signal is not checked.)
This printer employs 3 different transfer methods, which can be selected using the dip switches. (Refer to Chapter 1,
5-3 Setting Dip Switches)
(1) DTR method
The DTR signal is considered a BUSY signal at the handshake, and when the data buffer capacity is 256 bytes or
less, the DTR signal is given a marked status, meaning it cannot receive data. When the capacity of the data buffer
increases to 512 bytes or more during printing, the DTR signal is given a space status, which indicates that it can
receive data.
(2) X /X method
ON OFF
When a handshake is carried out with the host computer, the X
and DC3). (DC1 and DC3 are called X
19) is output to the TXD terminal, and the computer receives a request to stop data transfer. The printer outputs DC3
until it (the computer) stops data transfer. During printing, when the buffer full status is cancelled and data can be
received, DC1 (ASCII code 17) is output to the TXD terminal. When DC1 is output from the printer, the computer
follows the data format, and begins data transfer. Data transfer will continue until DC3 is output again.
(3) ETX/ACK method
The data block is configured as shown below, but the initial STX code is not necessary. When an STX code is sent
from the host computer, that 1 byte is ignored. When the ETX code is received, that 1 byte is not regarded as data,
an ACK or NACK code is sent to the TXD terminal, and the host computer is informed that data reception has been
completed.
Data block form:
STX
and X , respectively.) When the printer buffer is full, DC3 (ASCII code
ON OFF
DATA (8 KB or less)
Fig. 2-5 Data Format
– 22 –
/X method makes use of ASCII codes (DC1
ON OFF
ETX