MISE provides an RS-232 port that is functionally compatible to the Radio Shack add-on card for the original Expansion Interface. Refer to documentation for the Radio Shack RS-232 card for operational details.
There are a few differences from the original implementation:
The new I/O registers are summarized below:
Port 0xE6 (WO): Sense Switch Control Bit 7 - Sense switch 7 (even parity enable) Bit 6 - Sense switch 6 (word length select 1) Bit 5 - Sense switch 5 (word length select 2) Bit 4 - Sense switch 4 (stop bit select) Bit 3 - Sense switch 3 (parity inhibit) Bit 2 - Sense switch 2 (baud rate 3) Bit 1 - Sense switch 1 (baud rate 1) Bit 0 - Sense switch 0 (baud rate 2) Port 0xE6 (RO): Baud Rate Settings Bits 7:4 - Transmit baud rate Bits 3:0 - Receive baud rate Port 0xE7 (RO): UART Control Settings Bit 7 - Even parity enable Bit 6 - Word length select 1 Bit 5 - Word length select 2 Bit 4 - Stop bit select Bit 3 - Parity inhibit Bit 2 - Break Bit 1 - DTR* Bit 0 - RTS* Ports 0xE8-0xEB: Per Radio Shack implementation *Some Radio Shack documentation has these bits incorrectly reversed in its description of I/O port 0xEAH.
MIRE uses a standard male DE-9 connector for RS-232. There is also a PCB site for an optional 10-pin box header. Be careful if you decide to use this, since there are two common pinouts for RS-232 headers. The pinout used by MIRE is called "AT/Everex" and duplicates the pin numbers on the DE-9 connector: pin 1 on each is the same signal, so is pin 2, etc. There is fairly common on PC motherboards that provide for RS-232 ports on a separate bracket. Here is the pinout:
|DE-9 Pin||Header Pin||RS-232 Signal|
|1||1||DCD - Data Carrier Detect|
|2||2||RXD - Receive Data|
|3||3||TXD - Transmit Data|
|4||4||DTR - Data Terminal Ready|
|5||5||GND - System Ground|
|6||6||DSR - Data Set Ready|
|7||7||RTS - Request to Send|
|8||8||CTS - Clear to Send|
|9||9||RI - Ring Indicator|
The other common pinout is called "DTK/Intel" and the pin numbers are jumbled to make hookup easier. For example a simple crimped-on ribbon cable DE-9 connector uses this. It is incompatible with MIRE.
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