This converter may help if just the serial port on a personal computer is free, whereas the printer needs a parallel (Centronics) port. It converts a serial 2400 baud signal into a parallel signal.
The TxD line, pin 3, CTS line, pin 8, and the DSR line, pin 6, of the serial port, are used — see diagram. The CTS and DSR signals enable handshaking to be implemented.
Since the computer needs real RS232 levels, an adaptation from TTL to RS232 is provided in the converter by a MAX232. This is an integrated level converter that transforms the single +5 V supply into a symmetrical ±12 V one.
The serial-to-parallel conversion is affected by IC1. This is essentially a programmed PIC controller that produces a Centronics-compatible signal from a 2400 baud serial signal (eight data bits, no parity, one stop bit). The IC also generates the requisite control signals. If there is a delay on the Centronics port, the RS232 bitstream from the computer may be stopped via the Flow signal (pin 17). This ensures that no data is lost.
The controller needs a 4 MHz ceramic resonator, X1.
The MAX220– family of line drivers/receivers is intended for all EIA/TIA-232E and V.28/V.24 communications interfaces, particularly applications where ±12V is not available. The MAX225, MAX233, MAX235, and MAX245/MAX246/ MAX247 use no external components and are recommended for applications where printed circuit board space is critical. The MAX220-MAX249 are offered in 26 different packages
with temperatures from 0 to +70°C up to -55°C to +125°C. See the ordering information table at the end of the datasheet for all package and temperature options.
Features
- Meets or Exceeds TIA/EIA-232-F and ITU Recommendation V.28
- Operates From a Single 5-V Power Supply With 1.0-µF Charge-Pump Capacitors
- Operates up to 120 kbit/s
- Two Drivers and Two Receivers
- ±30-V Input Levels
- Low Supply Current: 8 mA Typical
- ESD Protection Exceeds JESD 22 – 2000-V Human-Body Model (A114-A)
- Upgrade With Improved ESD (15-kV HBM) and 0.1-µF Charge-Pump Capacitors are Available With the MAX202 Device
Applications
- TIA/EIA-232-F
- Battery-Powered Systems
- Terminals
- Modems
- Computers
