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Homebrew expansion RAM [message #79205] Sun, 02 June 2013 23:14
nessus is currently offline  nessus
Messages: 75
Registered: March 2013
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Message-ID: <1970@nsc.UUCP>
Date: Tue, 4-Dec-84 22:10:04 EST
Article-I.D.: nsc.1970
Posted: Tue Dec  4 22:10:04 1984
Date-Received: Fri, 18-Jan-85 01:52:12 EST
Distribution: net
Organization: The Patriarchy of Kzin
Lines: 99

*** REPLACE THIS LINE WITH YOUR MESSAGE ***


  1	+5V		Power		+5V Power for Speech Synthesizer
  2	SBE		Output		SPEECH BLOCK ENABLE CPU read from 90XXH
					or CPU write to 94XXH
  3	RESET/		Output		System reset
  4	EXTINT/		Input		EXTERNAL INTERRUPT User/expansion int.
  5	A5		Output		Address Bit 5
  6	A10		Output		Address Bit 10
  7	A4		Output		Address Bit 4
  8	A11		Output		Address Bit 11
  9	DBIN		Output		DATA BUS IN Hi=CPU read
 10	A3		Output		Address Bit 3
 11	A12		Output		Address Bit 12
 12	READY		Input		Set READY=Lo for wait states
 13	LOAD/		Input		Causes CPU to fetch new Program Counter
					& Workspace pointer from FFFCH & FFFEH
 14	A8		Output		Address Bit 8
 15	A13		Output		Address Bit 12
 16	A14		Output		Address Bit 12
 17	A7		Output		Address Bit 7
 18	A9		Output		Address Bit 9
 19	A15/CRUOUT	Output		Address Bit 15/CRU Data out(LS Address bit)
 20	A2		Output		Address Bit 2
 21	GND		Ground		Ground reference
 22	CRUCLK/		Output		CRU strobe
 23	GND		Ground		Ground reference
 24	PH3/		Output		3MHz clock
 25	GND		Ground		Ground reference
 26	WE/		Output		CPU write
 27	GND		Ground		Ground reference
 28	MBE/		Output		DSR access 4000H->5FFFH
 29	A6		Output		Address Bit 6
 30	A1		Output		Address Bit 1
 31	A0		Output		Address Bit 0(MS Address bit)
 32	MEMEN/		Output		Memory access
 33	CRUIN		Input		CRU read data
 34	D7		Bidirectional	Data Bit 7(LS Data bit)
 35	D4		Bidirectional	Data Bit 4
 36	D6		Bidirectional	Data Bit 6
 37	D0		Bidirectional	Data Bit 0(MS Data bit)
 38	D5		Bidirectional	Data Bit 5
 39	D2		Bidirectional	Data Bit 2
 40	D1		Bidirectional	Data Bit 1
 41	IAQ		Output		Instruction Acquisition Cycle
 42	D3		Bidirectional	Data Bit 3
 43	-5V		Power		-5V Power for Speech Synthesizer
 44	AUDIO IN	Input		User Audio input to sound generator

Gotchas:

1.  EVERY memory access consists of 2 sequential 8-bit accesses with odd
    (MS) byte written or read first.

2.  A0 is MOST SIGNIFACANT address bit.

3.  D0 is MOST SIGNIFICANT data bit.

       CPU       INT  EXP  BUS      EXP      Remarks
     Address     RAM  RAM  BUF    Address

   0000 -> 1FFF  Off  Off  Off  --Not Used--  Console ROM Access
   2000 -> 3FFF  Off  On   On   0000 -> 1FFF  Low EXP RAM Access
   4000 -> 5FFF  Off  Off  On   --Not Used--  DSR ROM Access
   6000 -> 7FFF  Off  Off  Off  --Not Used--  Cartridge Acess
   8000 -> 9FFF  On   Off  Off  --Not Used--  INT RAM/VDP/Speech Synth Access
   A000 -> BFFF  Off  On   On   2000 -> 3FFF  High EXP RAM Access
   C000 -> DFFF  Off  On   On   4000 -> 5FFF  High EXP RAM Access
   E000 -> FFFF  Off  On   On   6000 -> 7FFF  High EXP RAM Access
   0000 -> 1FFF  Off  Off  Off  --Not Used--  CRU Access

Data Path:

Data                    Data      _______________
Buffer                  Buffer   |               |
 _        Cable           _      | Expansion RAM |
|_|======================|_|=====|_______________|
 |                        |
 +------------------------+-------  

		
		
		
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