Macintosh LC 520 Developer Note

The Macintosh LC 520 Computer Developer Note is Apple's 1993 hardware description of the Macintosh LC 520, published by Apple's Developer Press for developers of compatible hardware and software. The hosted file is a 75-page PDF produced in March 1995. It covers the machine's features, architecture, expansion slot, ROM and system software, and internal storage bays, with an appendix on the AppleCD 300i drive. It is not a repair manual.

Contents

• Preface: About This Note (p. ix)
• Chapter 1, Introduction (p. 1): summary of features; comparisons with the Color Classic and LC III (pp. 2-3); integrated design and logic board access (pp. 3-4); built-in colour display, screen buttons and video RAM (pp. 4-6); power on and off, power saver (pp. 6-7); RAM expansion (p. 8); PDS expansion slot (p. 10); SCSI bus, termination and comparison of SCSI arrangements (pp. 10-12); floppy drive (p. 12); serial ports (p. 13); ADB (p. 15); sound, microphone and sound input jack (pp. 15-16); keyboard, reset and NMI (p. 16)
• Chapter 2, Architecture (p. 19): block diagram; MC68030; custom ICs Ardbeg, Ariel, Combo and Cuda; sound circuits (pp. 20-23); address map and video RAM (pp. 23-25); video display timing (p. 25)
• Chapter 3, Expansion (p. 29): slot pin assignments and signals (pp. 30-34); expansion card connectors, address space and power (pp. 34-36)
• Chapter 4, Software (p. 37): ROM software, machine identification (p. 38); system software, CD-ROM booting, Sound and Screen control panels, screen driver (pp. 40-44)
• Chapter 5, Internal Storage Devices (p. 45): slide-in bays, front drive bezel, connector adapters (pp. 46-48); internal CD-ROM drive dimensions, mounting and power (pp. 48-51)
• Appendix: AppleCD 300i Specifications (p. 53); Index (p. 55); foldouts (p. 59)

What it settles

• RAM: 4 MB on the board and one 72-pin SIMM socket for a 1 to 32 MB SIMM of 80 ns or faster, 36 MB in all (p. 8). The Service Source asks for 100 ns or faster.
• VRAM: 512 KB on the board plus one 68-pin socket for a 256 KB SIMM of 80 ns or faster, 768 KB in all, giving 16 bits per pixel (32,768 colours) on the built-in display (p. 6). The 1 MB figure in the shared Service Source applies to the LC 575.
• ROM: 1 MB in sockets, with provision for 2 MB (p. 2).
• SCSI termination: the internal end is terminated in the internal hard disk; the logic board switches in its own external-end terminator when no external device is attached and switches it out at system reset when external termination is detected (pp. 10-11). Apple lists the IIvx and Centris 650 as using the same arrangement (p. 12).
• Expansion slot: 114-pin, also taking 96-pin cards and the Apple IIe Card; a card may draw 1.0 A at +5 V, 20 mA at −5 V and 200 mA at +12 V, 5 W in all (pp. 10, 36).
• CD-ROM power: the AppleCD 300i is budgeted 500 mA at +5 V and 800 mA at +12 V, 1.5 A peak (p. 50).
• Ports: the modem port is a 9-pin mini-DIN socket with +5 V on pin 9, up to 100 mA; ADB and modem devices share 500 mA (pp. 14-15).
• Power: a master switch at the back must be on for the keyboard power key to work; switching the master switch off shuts the machine down without a safe shutdown (p. 6).
• Machine identification: gestaltMachineType 56 ($38) (p. 38).

What it does not contain

No schematic, no component values and no parts list. There is nothing on the analog board, power supply voltages or CRT adjustments, and nothing on the PRAM battery. For those, and for take-apart and symptom charts, see Macintosh LC 520/550/575 Service Source.

Pages that cite this document

• Macintosh LC 520 (memory, VRAM, SCSI termination, expansion and CD-ROM power)
• Macintosh LC 550

Download: Macintosh LC 520 Developer Note.pdf (811 KB)