MicroChannel Adapter Database
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Entry updated Feb 2006
 5FEC ::: QUATECH QS-2000 Quad Port Asynchronous RS-422
5FEC ::: QUATECH QS-3000 Quad Port Asynchronous RS-485

Adapter ID

Adapter ID
QUATECH QS-2000 Quad Port Asynchronous RS-422
QUATECH QS-3000 Quad Port Asynchronous RS-485
COM SER  Serial Port
QUAT  Quatech Inc.


Technical information contained in this page are edited excerpts from the QUATECH Reference Manual (qs-2000.pdf), Copyright © Quatech Inc.


Bus interfaceMicroChannel 16-bit
D-37 female connector *
Quad 6-wire RJ-11 (optional) *
Transmit driversMC3487
Receive buffersMC3486
I/O address range0000H - FFFFH (block mode)
Serial 1 - Serial 8 (discrete mode)
Interrupt levelsIRQ 3, 4, 9
Power requirements
1425mA typical, 1618mA maximum at +5V
Power requirements
1372mA typical, 1566mA maximum at +5V

* Connector pinouts are described in the QS-2000/QS-3000 Reference Manual.


The Quatech (Qua Tech) QS-2000 provides four independent asynchronous RS-422 serial communication channels for systems utilizing the MicroChannel architecture. The QS-3000 is an RS-485 version of the adapter. Each port may be accessed individually from the predefined addresses of Serial 1 through Serial 8 or the four channels may be grouped together and located anywhere within the available I/O address range of the system. Two output options increase flexibility by allowing connection to a 37-pin 'D' connector (D-37) or an abbreviated 6-wire RJ-11 modular phone jack style connector.

The QS-2000/QS-3000 serial interface is realized through four 16550 ACEs (Asynchronous Communication Elements). The 16550 is compatible with the 8250 and 16450 ACEs used in the PC/XT/AT models. In addition, the 16550 supports a FIFO mode to reduce CPU overhead at higher data rates.

The QS-2000/QS-3000 address and interrupt selections are accessed through the Programmable Option Select using the IBM installation utilities. In addition, jumpers are provided to select input clock frequency and control of the data exchanged on the auxiliary channel.

16550 Features

The 16550 is an upgrade of the standard 16450 Asynchronous Communications Element (ACE). Designed to be compatible with the 16450, the 16550 enters the character mode on reset and in this mode will appear as a 16450 to user software. An additional mode, FIFO mode, can be selected to reduce CPU overhead at high data rates. The FIFO mode increases performance by providing two internal 16-byte FIFOs (one transmit and one receive) to buffer data and reduce the number of interrupts issued to the CPU.

Baud Rate Selection

The 16550 ACE determines the baud rate of the serial output from a combination of the clock input frequency and the value written to the divisor latches. Standard PC, PC/XT, PC/AT, and PS/2 serial interfaces use an input clock of 1.8432 MHz. To increase versatility, the QS-2000/QS-3000 uses an 18.432 MHz clock and a frequency divider circuit to produce the standard clock frequency.

Jumper block J5 is used to set the input frequency to the 16550. It may be connected to divide the clock input by 1, 2, 5, or 10. To maintain compatibility with adapters using a 1.8432 MHz input, J1 should be configured to divide by 10. Consult the QS-2000/QS-3000 Reference Manual for the table of divisor latch values for various input frequencies.

Addressing Options

Each channel of the QS-2000/QS-3000 uses eight consecutive I/O address locations beginning on an even 8 byte boundary (xxx0H - xxx7H) or (xxx8H - xxxFH). Two addressing modes are available on the QS-1000: discrete addressing and block addressing.

  • Discrete Addressing Mode In the discrete addressing mode, each port may choose an individual base address. This mode allows maximum compatibility with software supporting the pre-defined addresses for Serial 1 through Serial 8. Channels 1 and 2 may select from Serial 1 through Serial 7, Channels 3 and 4 may choose from Serial 2 through Serial 8. Each channel may be individually disabled.

  • Block Addressing Mode In block addressing mode, the four serial channels are arranged to form a continous 32-byte block I/O addresses. This mode offers more compactness for custom software applications. The block may be placed anywhere in the available I/O address range on an even 32-byte boundary (e.g. 400H - 41FH , 620H - 63FH , 4980H - 499FH ) using the IBM installation utilities and the Qua Tech address installation utility QTINSTAL.EXE.

    WARNING: In block mode, each channel may be individually disabled, but the I/O space assigned to that channel is still considered in use and may not be used by another device.

NOTE: To change the addressing mode, physically remove the QS-2000/QS-3000 from the system, configure the system with the reference diskette, physically reinsert the QS-2000/QS-3000 and configure again the system with the reference diskette (UZ).

Output Configurations

Four sets of jumpers are implemented on the QS-2000/QS-3000 to control the auxiliary driver/receiver set. J1 through J4 perform the identical functions on channels 1 through 4 respectively.

Auxiliary Channel Configuration

The following discussion pertains to the control of the information exchanged on the auxiliary channel of the QS-2000/QS-3000. Since the auxiliary channel is not supported with the RJ-11 connector option, these users should set jumpers J1 - J4 to loopback all of the auxiliary channel signals and skip to "Half Duplex Operation".

The function of J1 through J4 is to control the source of the information exchanged on the auxiliary communication lines. The output sources are request to send (RTS), transmit clock (XCLK), and the auxiliary input (AUX IN). The inputs are clear to send (CTS) and receive clock (RCLK).

Transmission of RTS, when combined with reception of CTS, allows for handshaking between the 1650 and a peripheral device. RTS is transmitted by connecting pins 5 and 6 of the jumper block. CTS is received by connecting pins 1 and 2. The RTS/CTS handshake can be defeated by looping the RTS output back to the CTS input. This is accomplished by connecting pins 1 and 5.

RCLK is the input to the 16550 that controls the shift rate of the receiver portion of the chip. Generally, this input is provided by connecting it to the transmit clock, XCLK, output from the ACE. This is accomplished by connecting pins 3 and 7 of the jumper. RCLK may be received from an external source by connecting pins 2 and 3. Transmission of XCLK can be used to synchronize communications with a peripheral or to provide a shift clock to a receiver. XCLK is transmitted by connecting pins 6 and 7 of the jumper block.

AUX IN is the auxiliary input from a peripheral device. Connecting AUX IN to AUX OUT provides a loopback mode of operation. That is, whatever is transmitted by the peripheral will be fed back to the peripheral. This is implemented by connecting pins 2 and 6 of the jumper block.

Half Duplex Operation

The other function of J1 through J4 is to configure the communication channel in half or full duplex mode. Half duplex operation is achieved by connecting pins 4 and 8 of the jumper block. This allows the transmitter to be enabled and disabled using the data terminal ready (DTR) output controlled through the modem control register. When DTR is set (logic 1), the transmitter driver is enabled for both the data and auxiliary channel output. When cleared (logic 0), both outputs enter high impedance states. Full duplex communication is restored by removing the jumper on pins 4 and 8.

CAUTION: When operating in half duplex mode, the transmitter must be disabled before receiving any information. Failure to do so will result in two output drivers being connected together which may cause damage to the adapter, the computer, and/or the peripheral equipment.

External Connections

The QS-2000/QS-3000 is available with two output configurations. The first option uses a female D-37 connector labeled CN1 on the circuit board. This configuration can provide all of the signals for each channel. The second option uses a quad 6-wire RJ-11 phone jack style connector labeled CN2 on the circuit board. This configuration provides only transmit and receive. Both output configurations have optional adapter cables to provide standard D-25 connectors for each channel. The various connectors and pinouts are described in detail in the QS-2000/QS-3000 Reference Manual.


DOS drivers and utilities (QTINSTAL.EXE): ftp://quatech.com/Communication/Qs-2000.zip


Reference manual: ftp://quatech.com/manuals/qs-2000.pdf

ADF Adapter Description File


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