Macintosh Hardware Memory Map

----- CONFIDENTIAL ------------------------------------------ CONFIDENTIAL ----MACINTOSH HARDWARE MEMORY MAP Burrell Smith and Brian Howard 13 April 1983 ----- CONFIDENTIAL ------------------------------------------ CONFIDENTIAL ----Page 1 1. INTRODUCTION Page 2 2. MEMORY MAP ON POWER-UP (OVERLAY = 1) Page 3 3. NORMAL MEMORY MAP (OVERLAY = 0) Page 4 4. RAM 4.1 Address Decoding to Activate RAMs 4.2 Some Useful RAM Addresses 4.3 More Detailed Map of RAM 4.4 Hardware Exception Vectors Page 5 Page 6 Page 7 5. ROM 5.1 Address Decoding to Activate ROMs 5.2 Useful ROM Addresses Page 8 6. SCC 6.1 Address Decoding to Activate SCC 6.2 Further SCC Address Decoding 6.3 Some Useful SCC Addresses Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 7. IWM 7.1 Address Decoding to Activate IWM 7.2 Further IWM Address Decoding 7.3 Some Useful IWM Addresses 8. VIA 8.1 Address Decoding to Activate VIA 8.2 Further VIA Address Decoding 8.3 Some Useful VIA Addresses 8.4 Macintosh-Specific Information about VIA Registers 8.4.1 Port A Input, Output, and Data Direction Registers 8.4.2 Port B Input, Output, and Data Direction Registers 8.4.3 Control Registers 8.4.4' Interrupt Flag and Enable Registers 9. PHASE READ 9.1 Address Decoding to Activate PHASE READ 9.2 Further PHASE READ Address Decoding 9.3 Using PHASE READ Page 18 10. AUTO-VECTOR "READ" ADDRESSES Page 19 11. SOME USEFUL DECODING EQUATIONS 13 April 1983 1. Macintosh Memory Map Page 1 INTRODUCTION The principle portions of Macintosh's memory consist of volatile read/write memory (RAM) and permanent read-only memory (ROM). In addition to RAM and ROM, three input/output devices are also selected using address lines, so that they appear to occupy portions of the Macintosh memory space. These devices are the 6522 Versatl~e Interface Adapter (VIA), the 8530 Serial Communications,Chip (SCC), and the disk interface chip (IWM). When the Macintosh is first turned on, ROM appears at ehe bottom (lowest -- >-"1 addresses) portion of the memory space. This is useful for the ROM-stored software which starts the system running. Afte~·tup, the OVERLAY signal from the VIA is changed to a low (zero), mapping RAM into its normal place at the bottom of memory. Selection of RAM, ROM, or other devices is done by from two to five of the highest-order address lines, A23-A19. The VIA and IWM also use the four address lines A12-A9 for further internal decoding and register selection, while the SCC uses the three lowest-order address lines A2-A0 for internal decoding. In specifying "useful addresses" for most devices, unused address lines have been set high (to a one) to save a small amount of power and to improve noise immunity. Some address ranges are specified "Do Not Use" because they can select two devices simultaneously. While this does not cause any damage to the computer, data cannot be correctly transferred while these addresses are in use. 13 April 1983 2. Page 2 Macintosh Memor…