New Micros Inc. (NMI) NMIS-L-5002 serial communications board
2x4"s[tm] 2 channel, R65C52 based RS232
The NMIS-5002 Dual ACIA Card, in 2x4"s[tm] format, provides a JEDSTACK[tm] computer system with two Asynchronous Serial Channels, at full RS-232C/V.28 levels.
- Two independent, full-duplex RS-232 channels with buffered receivers and transmitters
- Data set/modem control functions
- Baud rate generator with 15 programmable baud rates (50 to 38,400)
- Programmable word lengths, number of stop bits, and parity bit generation and detection
- Programmable interrupt control
- Programmable control of edge detect for DCD, DSR, DTR, RTS, and CTS
- Automatic Address Recognition Mode for multidrop operation
Each of the channels has a 26-pin, IDC style, male header that accepts a common cable, with a 26-pin female IDC and a DB-25, to connect the board to other communications equipment. This cable was chosen because of its widespread availability. Jumpers are provided to allow the choice of selecting Data Terminal (DTE) or Data Set Equipment (DSE) configurations. This eliminates the need for an additional null-modem.
The Dual ACIA chip, a Rockwell 65C52, is the key part on the board. It generates the outgoing serial data and translates the incoming data in processor readable form. The ACIA channels can be interrupt driven to allow minimum processor overhead.
A Vertical Stacking Connector in the lower right hand corner (top view) provides connections to the processor's address and data bus, control signals, 5V power and ground. Address decoding of the Dual ACIA chip's space in memory is accomplished by two octal comparators and 16 two-position jumpers. Each jumper setting corresponds to the state of a particular address line. The NMIS-5002 occupies 8 addresses. Any 8-byte boundary in the 64K address space of the JEDSTACK[tm] processor's bus can be selected by correct jumper placement.
The DACIA has an internal baud rate generator. The transmitter baud rate is programmable to any one of 15 different rates from 50 to 38,400 baud. The DACIA is programmable for word lengths of 5,6,7 or 8 bits; even, odd, or no parity; and 1 or 2 stop bits.
The RS-232 level shifting is provided by three chips. The ICL232CPE is a charge pump producing the elevated +9V and -9V needed for RS-232 communications from a single +5V supply. It also contains two pairs of RS-232 line drivers. The MC145406's each contain an additional three pairs of line drivers . These chips convert the CMOS serial data lines to RS-232 levels.