RS-232 Port

MIRE 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
11DCD - Data Carrier Detect
22RXD - Receive Data
33TXD - Transmit Data
44DTR - Data Terminal Ready
55GND - System Ground
66DSR - Data Set Ready
77RTS - Request to Send
88CTS - Clear to Send
99RI - Ring Indicator
-10No Connection

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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