System RAM - Revision history

Mr z: Protected "System RAM" ([edit=autoconfirmed] (indefinite) [move=autoconfirmed] (indefinite))

2010-12-04T09:35:00Z

Protected "System RAM" ([edit=autoconfirmed] (indefinite) [move=autoconfirmed] (indefinite))

Mr z: /* EXEC and System RAM */

2007-10-09T23:33:51Z

‎EXEC and System RAM

Arnauld at 07:33, 1 February 2005

2005-02-01T07:33:38Z

Mr z: /* Quirks */

2005-01-23T23:02:38Z

‎Quirks

Mr z: /* EXEC and System RAM */

2005-01-23T23:00:57Z

‎EXEC and System RAM

Mr z: /* Quirks */

2005-01-23T22:58:14Z

‎Quirks

Mr z: /* Quirks */

2005-01-23T22:35:48Z

‎Quirks

Mr z at 22:34, 23 January 2005

2005-01-23T22:34:44Z

Mr z at 22:33, 23 January 2005

2005-01-23T22:33:50Z

Mr z at 22:22, 11 January 2005

2005-01-11T22:22:58Z

@@ Line 11: / Line 11: @@
 <table border>
-<tr><td>$0200-$02EF</td><td>BACKground TABle (BACKTAB), fixed by the hardware</td></tr>
+<tr><td>$0200-$02EF</td><td>BACKground TABle ([[BACKTAB]]), fixed by the hardware</td></tr>
 <tr><td>$02F0      </td><td>[[Executive ROM|EXEC]]:  Indicates the currently active cartridge header.</td></tr>
-<tr><td>$02F1-$0318</td><td>CP1610 Stack. (Upper bound actually determined by the game software.)</td></tr>
+<tr><td>$02F1-$0318</td><td>EXEC: CP1610 Stack. (Upper bound actually determined by the game software.)</td></tr>
 <tr><td>$0319-$031C</td><td>EXEC: Unknown use</td></tr>
 <tr><td>$031D-$035C</td><td>EXEC: MOB RAM data base</td></tr>

@@ Line 16: / Line 16: @@
 <tr><td>$0319-$031C</td><td>EXEC: Unknown use</td></tr>
 <tr><td>$031D-$035C</td><td>EXEC: MOB RAM data base</td></tr>
-<tr><td>$035D</td><td>EXEC: Current hand controller dispatch table pointer</td></tr>
+<tr><td>$035D</td><td>EXEC: Current [[Hand Controller]] dispatch table pointer</td></tr>
 <tr><td>$035E</td><td>EXEC: Current random number seed</td></tr>
 <tr><td>$035F</td><td>EXEC: Something sound related</td></tr>

@@ Line 24: / Line 24: @@
 ==Quirks==
-The System RAM does not correctly implement the ADAR [[Bus Phases|Bus Phase]].  Thus, while program code can execute out of System RAM, not all opcodes function correctly.  Specifically, [[Direct Mode]] instructions do not work correctly when executed from System RAM.
+The System RAM does not correctly implement the ADAR [[Bus Phases|Bus Phase]].  Thus, while program code can execute out of System RAM, [[Direct Mode]] instructions do not work correctly when executed from System RAM.
 <br/><br/>
 The System RAM uses the [[Bus Phases|INTAK Bus Phase]] to switch into [[Bus Copy]] mode.  It uses the BUSAK signal from the CPU to switch out of [[Bus Copy]] mode.  Incorrect programs can cause the CPU not to issue BUSAK in response to a BUSRQ from the STIC.  (This is accomplished by having a suitably long sequence of non-interruptible instructions while BUSRQ is high.)  As a result, the System RAM could stay in [[Bus Copy]] mode during at least part of active display, leading to potentially harmful "bus fights" between the STIC and the System RAM.  The display gets corrupted rather impressively as a result.  Specially designed test programs have verified this phenomenon.

@@ Line 11: / Line 11: @@
 <table border>
-<tr><td>$0200-$02EF</td><td>BACKground TABle (BACKTAB)</td></tr>
+<tr><td>$0200-$02EF</td><td>BACKground TABle (BACKTAB), fixed by the hardware</td></tr>
-<tr><td>$02F0-$02F0</td><td>[[Executive ROM|EXEC]]:  Indicates the currently active cartridge header</td></tr>
+<tr><td>$02F0      </td><td>[[Executive ROM|EXEC]]:  Indicates the currently active cartridge header.</td></tr>
 <tr><td>$02F1-$0318</td><td>CP1610 Stack. (Upper bound actually determined by the game software.)</td></tr>
 <tr><td>$0319-$031C</td><td>EXEC: Unknown use</td></tr>

@@ Line 25: / Line 25: @@
 The System RAM does not correctly implement the ADAR [[Bus Phases|Bus Phase]].  Thus, while program code can execute out of System RAM, not all opcodes function correctly.  Specifically, [[Direct Mode]] instructions do not work correctly when executed from System RAM.
 <br/><br/>
 The RA-3-9600 and RA-3-9600A varieties of the System RAM are both functionally equivalent.  However, the RA-3-9600A has an additional quirk.  Rather than strictly decoding itself into the address range $200 - $35F, it decodes itself into the larger range $200 - $3FF.  As a result, it responds to accesses in the range $360 - $3FF.  The exact values the chip returns appear meaningless, and they vary from chip to chip.  Programs should not rely on accesses to addresses $360 - $3FF returning $FFFF.

← Older revision	Revision as of 09:35, 4 December 2010
(No difference)

@@ Line 5: / Line 5: @@
 * It holds the BACKTAB (Background Table) that defines the screen's image.
 <br />
 ==EXEC and System RAM==
 Programs which rely heavily on the [[Executive ROM]] cannot use most of the storage in System RAM.  The display background occupies most of System RAM, and the EXEC's variables and data structures occupy the rest.  Some EXEC-based games do store variables here through various tricks, such as limiting the number of active MOBs to fewer than 8, or by blanking the first row of the display to make $200 - $213 available.  (Advanced Dungeons and Dragons Tarmin Treasure does the latter trick.)  Programs that utilize the EXEC minimally, if at all can allocate all of $2F0 - $35F as they see fit.<br /><br />
@@ Line 22: / Line 20: @@
 <tr><td>$035F</td><td>EXEC: Something sound related</td></tr>
 </table>
 ==Quirks==
-The System RAM does not correctly implement the ADAR [[Bus Phase]].  Thus, while program code can execute out of System RAM, not all opcodes function correctly.  Specifically, [[Direct Mode]] instructions do not work correctly when executed from System RAM.
+The System RAM does not correctly implement the ADAR [[Bus Phases|Bus Phase]].  Thus, while program code can execute out of System RAM, not all opcodes function correctly.  Specifically, [[Direct Mode]] instructions do not work correctly when executed from System RAM.
 The RA-3-9600 and RA-3-9600A varieties of the System RAM are both functionally equivalent.  However, the RA-3-9600A has an additional quirk.  Rather than strictly decoding itself into the address range $200 - $35F, it decodes itself into the larger range $200 - $3FF.  As a result, it responds to accesses in the range $360 - $3FF.  The exact values the chip returns appear meaningless, and they vary from chip to chip.  Programs should not rely on accesses to addresses $360 - $3FF returning $FFFF.

@@ Line 1: / Line 1: @@
 [[Category:Memory Units]]
-The System RAM unit is the only 16-bit RAM available in the Intellivision, and it is mapped into the Intellivision [[Memory Map|memory map]] from $0200-$035F.  The System RAM has these additional responsibilities:<br/>
+The System RAM resides in a single [[General Instruments|GI]] RA-3-9600 (Intellivision I) or RA-3-9600A (Intellivision II onwards).  The System RAM unit is the only 16-bit RAM available in the Intellivision, and it is mapped into the Intellivision [[Memory Map|memory map]] from $0200-$035F.  The System RAM has these additional responsibilities:<br/>
 * It bridges between the STIC's private graphics bus and the CPU's main memory bus.  This additional functionality is described under [[Bus Copy]].
 * It provides a 20-word Video FIFO to reduce the STIC's [[STIC Bus Request|memory bandwidth impact]] on the System RAM.
 <br />
 Programs which rely heavily on the [[Executive ROM]] cannot use most of the storage in System RAM.  The display background occupies most of System RAM, and the EXEC's variables and data structures occupy the rest.  Some EXEC-based games do store variables here through various tricks, such as limiting the number of active MOBs to fewer than 8, or by blanking the first row of the display to make $200 - $213 available.  (Advanced Dungeons and Dragons Tarmin Treasure does the latter trick.)  Programs that utilize the EXEC minimally, if at all can allocate all of $2F0 - $35F as they see fit.<br /><br />
@@ Line 18: / Line 22: @@
 <tr><td>$035F</td><td>EXEC: Something sound related</td></tr>
 </table>