DB25 D-sub connector engineering reference

IBM figure shows the adapter's 25-pin connector (1-13 / 14-25); directions as drawn relative to the adapter.

• P115 DB25 — **Agree** on the PC parallel port (1 −Strobe, 2–9 data 0–7, 10 −ACK, 11 Busy, 12 PE, 13 Select, 14 −Auto Feed, 15 −Error, 16 −Init, 17 −Select In, 18–25 ground) and the IBM PS/2 serial port on all main signals — **One documented difference: serial pin 11.** A's PS/2 Hardware Interface reference says not connected; B's PS/2 Model 25 reference says "tied to line 20" (DTR). These are different IBM documents and models, so record pin 11 as model-specific, not a conflict to resolve. B's SMSC FDC37C669 signal names stay unverified because that datasheet doesn't tie them to a DB25. A adds the Mac Plus SCSI port as an unrelated DB25 use.
• TIA-232-F is paywalled; only the IBM PS/2 DTE subset is verified.
• IEEE 1284 is paywalled; host parallel rows rely on IBM.
• Sun/Apple serial, audio multicore (AES59/Tascam), and other uses not established.

IBM drawing numbers 13...1 on the top row and 25...14 on the bottom row (receptacle face as drawn).

• P115 DB25 — **Agree** on the PC parallel port (1 −Strobe, 2–9 data 0–7, 10 −ACK, 11 Busy, 12 PE, 13 Select, 14 −Auto Feed, 15 −Error, 16 −Init, 17 −Select In, 18–25 ground) and the IBM PS/2 serial port on all main signals — **One documented difference: serial pin 11.** A's PS/2 Hardware Interface reference says not connected; B's PS/2 Model 25 reference says "tied to line 20" (DTR). These are different IBM documents and models, so record pin 11 as model-specific, not a conflict to resolve. B's SMSC FDC37C669 signal names stay unverified because that datasheet doesn't tie them to a DB25. A adds the Mac Plus SCSI port as an unrelated DB25 use.
• I/O column: pins 1-9 'I/O', 10-13 'I', 14/16/17 'O', 15 'I', 18-25 'NA'. Data lines are bidirectional in extended mode.
• TIA-232-F is paywalled; only the IBM PS/2 DTE subset is verified.
• IEEE 1284 is paywalled; host parallel rows rely on IBM.
• Sun/Apple serial, audio multicore (AES59/Tascam), and other uses not established.

IBM drawing numbers 1...13 top row, 14...25 bottom row (as drawn).

• P115 DB25 — **Agree** on the PC parallel port (1 −Strobe, 2–9 data 0–7, 10 −ACK, 11 Busy, 12 PE, 13 Select, 14 −Auto Feed, 15 −Error, 16 −Init, 17 −Select In, 18–25 ground) and the IBM PS/2 serial port on all main signals — **One documented difference: serial pin 11.** A's PS/2 Hardware Interface reference says not connected; B's PS/2 Model 25 reference says "tied to line 20" (DTR). These are different IBM documents and models, so record pin 11 as model-specific, not a conflict to resolve. B's SMSC FDC37C669 signal names stay unverified because that datasheet doesn't tie them to a DB25. A adds the Mac Plus SCSI port as an unrelated DB25 use.
• IBM: 'standard D-shell connector and pin assignments defined for RS-232C', EIA voltage levels only, no current loop.
• TIA-232-F is paywalled; only the IBM PS/2 DTE subset is verified.
• IEEE 1284 is paywalled; host parallel rows rely on IBM.
• Sun/Apple serial, audio multicore (AES59/Tascam), and other uses not established.

Pin numbers from Apple's table; no face view.

• P115 DB25 — **Agree** on the PC parallel port (1 −Strobe, 2–9 data 0–7, 10 −ACK, 11 Busy, 12 PE, 13 Select, 14 −Auto Feed, 15 −Error, 16 −Init, 17 −Select In, 18–25 ground) and the IBM PS/2 serial port on all main signals — **One documented difference: serial pin 11.** A's PS/2 Hardware Interface reference says not connected; B's PS/2 Model 25 reference says "tied to line 20" (DTR). These are different IBM documents and models, so record pin 11 as model-specific, not a conflict to resolve. B's SMSC FDC37C669 signal names stay unverified because that datasheet doesn't tie them to a DB25. A adds the Mac Plus SCSI port as an unrelated DB25 use.
• Included to show that DB-25 carries unrelated interfaces; signals with '-' are active-low.
• TIA-232-F is paywalled; only the IBM PS/2 DTE subset is verified.
• IEEE 1284 is paywalled; host parallel rows rely on IBM.
• Sun/Apple serial, audio multicore (AES59/Tascam), and other uses not established.

D-sub contact numbers 1-25 as moulded. IBM Model 25 drawings are 'viewed from the rear of the system unit': serial shows pin 1 top-left (pin face), parallel shows pin 1 top-right (socket face).

• P115 DB25 — **Agree** on the PC parallel port (1 −Strobe, 2–9 data 0–7, 10 −ACK, 11 Busy, 12 PE, 13 Select, 14 −Auto Feed, 15 −Error, 16 −Init, 17 −Select In, 18–25 ground) and the IBM PS/2 serial port on all main signals — **One documented difference: serial pin 11.** A's PS/2 Hardware Interface reference says not connected; B's PS/2 Model 25 reference says "tied to line 20" (DTR). These are different IBM documents and models, so record pin 11 as model-specific, not a conflict to resolve. B's SMSC FDC37C669 signal names stay unverified because that datasheet doesn't tie them to a DB25. A adds the Mac Plus SCSI port as an unrelated DB25 use.
• IEEE 1284 is paywalled and was not read; EPP/ECP names come only from the SMSC datasheet table and are not tied to the DB25 shell by that document.
• TIA-232-F is paywalled and was not read; the serial variant is IBM Model 25 device-specific (only 10 functional pins wired).
• Mac SCSI (see Apple HW10 Figure 2, not recorded), DCE/modem side, synchronous RS-232 pins and other uses were not recorded.

D-sub contact numbers 1-25 as moulded. IBM Model 25 drawings are 'viewed from the rear of the system unit': serial shows pin 1 top-left (pin face), parallel shows pin 1 top-right (socket face).

• P115 DB25 — **Agree** on the PC parallel port (1 −Strobe, 2–9 data 0–7, 10 −ACK, 11 Busy, 12 PE, 13 Select, 14 −Auto Feed, 15 −Error, 16 −Init, 17 −Select In, 18–25 ground) and the IBM PS/2 serial port on all main signals — **One documented difference: serial pin 11.** A's PS/2 Hardware Interface reference says not connected; B's PS/2 Model 25 reference says "tied to line 20" (DTR). These are different IBM documents and models, so record pin 11 as model-specific, not a conflict to resolve. B's SMSC FDC37C669 signal names stay unverified because that datasheet doesn't tie them to a DB25. A adds the Mac Plus SCSI port as an unrelated DB25 use.
• IEEE 1284 is paywalled and was not read; EPP/ECP names come only from the SMSC datasheet table and are not tied to the DB25 shell by that document.
• TIA-232-F is paywalled and was not read; the serial variant is IBM Model 25 device-specific (only 10 functional pins wired).
• Mac SCSI (see Apple HW10 Figure 2, not recorded), DCE/modem side, synchronous RS-232 pins and other uses were not recorded.

SMSC Table36 HOSTCONNECTOR numbers1-17 only. This document does not establish DB25 shell identity, pins18-25, or a physical mating-face/rear view; IBM Model25 drawings are a different implementation.

• P115 DB25 — **Agree** on the PC parallel port (1 −Strobe, 2–9 data 0–7, 10 −ACK, 11 Busy, 12 PE, 13 Select, 14 −Auto Feed, 15 −Error, 16 −Init, 17 −Select In, 18–25 ground) and the IBM PS/2 serial port on all main signals — **One documented difference: serial pin 11.** A's PS/2 Hardware Interface reference says not connected; B's PS/2 Model 25 reference says "tied to line 20" (DTR). These are different IBM documents and models, so record pin 11 as model-specific, not a conflict to resolve. B's SMSC FDC37C669 signal names stay unverified because that datasheet doesn't tie them to a DB25. A adds the Mac Plus SCSI port as an unrelated DB25 use.
• Table 36 numbers 'HOST CONNECTOR' pins 1-17 but does not name the shell (DB25) or list pins 18-25; rows are therefore unverified for this connector record.
• IEEE 1284 is paywalled and was not read; EPP/ECP names come only from the SMSC datasheet table and are not tied to the DB25 shell by that document.
• TIA-232-F is paywalled and was not read; the serial variant is IBM Model 25 device-specific (only 10 functional pins wired).
• Mac SCSI (see Apple HW10 Figure 2, not recorded), DCE/modem side, synchronous RS-232 pins and other uses were not recorded.