122 lines
5.3 KiB
Plaintext
122 lines
5.3 KiB
Plaintext
MiniSport Laptop Hacker - Vol 8
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28 Feb 93
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>>> POOR MAN'S PACKET (PMP) ON THE MINISPORT.
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Hallelujah! I got it working! I have a complete TNC built on a little
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perfboard. It slides in the left side of the MiniSport in place of the
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land-line modem Zenith sold with the computer. As soon as I finish the
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series on the COMx: ports, I'll cover how this information was used to make
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a complete packet station *inside* the MiniSport (minus a handheld).
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>>> MINISPORT LAPTOP COM2 PINOUT
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Take the cover off the modem slot on the left side of your MiniSport. If
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you have a modem in place, slide it out. Inside you'll see a 16-pin con-
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nector:
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1 3 5 7 9 11 13 15 (Viewed looking in the slot, right side up)
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2 4 6 8 10 12 14 16
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The pins are as follows:
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1 +5v output
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2 +10v output
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3 -10v output
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4 GND
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5 TTL signal (or power supply?). High when CMOS setup turns COM2 on.
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Alternately the command line MACHINE MODEM ON lets you set it to high;
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MACHINE MODEM OFF sets it to low.
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6 Carrier Detect, TTL input.
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7 Received Data, TTL input.
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8 GND
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9 Transmit Data, TTL output.
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10 Associated with the built-in computer speaker. Touching to +5v
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through a 1kohm resister makes the speaker squawk.
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11 ?? ground ??
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12 Ring Indicator, TTL input.
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13 Data Terminal Ready, TTL output.
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14 Clear to Send, TTL input.
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15 Request to Send, TTL output.
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16 Data Set Ready, TTL input.
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>>> COM I/O ARCHITECTURE
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In Volume 7, the addresses of the COM I/O ports were given. Now I'll start
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discussing to what each of the nine registers actually allows access. I'll
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refer to a BASE address. In the case of COM1, this is 0x03F8. In the case
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of COM2, this is 0x02F8. I'll cover them in relative order of popularity.
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Receiver Buffer Register and Transmitter Holding Register (BASE+0)
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------------------------------------------------------------------
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These two registers appear at the same address. The receive buffer is read
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only; the transmit buffer is write only (makes sense!). This is where you
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read the actual byte received over the COM port or where you write the data
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you want to send out over the COM port.
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CAUTION: BASE+0 will access these registers if and only if the most signif-
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icant bit of the LCR (BASE+3) is zero.
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Modem Control Register (BASE+4)
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-------------------------------
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This register allows you to control certain output wires from the 8250.
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Normally, you'll write to this address, but you can read the register back
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in if you want to find the state of certain bits.
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Bit 0: This bit controls the Data Terminal Ready output. When set to a 1,
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DTR is "true." This corresponds to a low TTL level, normally in-
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verted to become +12v at pin 4 of a DB-9 connector. PMP oscillates
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this line to control the mark/space output of the modem. When this
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bit is set to 0, PMP receives a high TTL level, providing a 1200Hz
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mark frequency.
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Bit 1: This bit controls the Request to Send output. When set to a 1, RTS
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is "true." This corresponds to a low TTL level, normally inverted
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to become +12v at pin 7 of a DB-9 connector. PMP uses this as the
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PTT line output. PMP Key down is selected by writing a 0 to this
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bit.
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Bit 2: This controls an OUT1 line, not normally used in the PC environment.
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The output is inverted like the above two. Setting the bit to 0
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(zero) gives high TTL output.
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Bit 3: This controls an OUT2 line, not normally used in the PC environment.
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The output is inverted like the above lines. Setting the bit to 0
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(zero) gives high TTL output.
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Bit 4: Provides a loopback feature. Set to 0 for normal operation.
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Bit 5 - 7: Writing to these has no effect. Reading these bits will always
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provide 0 (zero).
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Modem Status Register (BASE+6)
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------------------------------
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This register lets you check on the status of certain control lines re-
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ceived by your computer.
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Bit 0 - 3: These are edge sensitive versions of the following four bits.
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Whenever any of the following four bits change state, the
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corresponding bit from this set goes to 1. Reading the MSR sets all
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four bits back to zero.
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Bit 4: This Clear to Send (CTS) bit is 1 when a low TTL level is presented
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to the UART. This normally corresponds to a +12v received on pin 8
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of the IBM/PC 9-pin connector. Used by PMP to monitor the
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mark/space status of the data stream coming in. An incoming space
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(2200Hz) will give a 1 when you read this bit.
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Bit 5: Data Set Ready (DSR) is 1 when a low TTL is presented to the UART,
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corresponding to pin 6 of the DB-9 being held at +12v. PMP uses this
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as a Carrier Detect line. It expects a 0 when the modem is receiv-
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ing either a mark or space tone.
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Bit 6: Ring Indicator. Logic the same as above two, provided into pin 9 of
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the DB-9 by whatever is hooked to it.
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Bit 7: Received Line Signal Detect. Logic is the same as above three, with
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no normal connection in the IBM/PC environment.
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>>> UPCOMING
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8250 DOCS, SERIAL & PARALLEL BUFFER CHIP PINOUTS, PMP SCHEMATIC, SHRINKING
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YOUR FAVORITE SOFTWARE, MINIMUM BOOT FILES, BOARD REVISIONS, and more DIS-
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ASSEMBLY.
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73, Brian, ka9snf@wb7nnf.#spokn.wa or Internet ka9snf@jupiter.spk.wa
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