Category:83Plus:Ports:By Address:Protected - Revision history

Brandonw: Whoops

2012-10-15T21:35:17Z

Whoops

Sircmpwn: /* Protected Ports */ finishing the changes to protected port information

2011-08-08T19:01:15Z

‎Protected Ports: finishing the changes to protected port information

Sircmpwn at 19:00, 8 August 2011

2011-08-08T19:00:29Z

130.215.239.90: /* Protected Ports */ alternatives to nop

2006-01-28T19:35:25Z

‎Protected Ports: alternatives to nop

Aquanight: "On the 84+ the pages are 6F..." 84+ what? :-)

2005-04-02T00:50:53Z

"On the 84+ the pages are 6F..." 84+ what? :-)

FloppusMaximus at 22:04, 29 March 2005

2005-03-29T22:04:18Z

FloppusMaximus at 21:53, 29 March 2005

2005-03-29T21:53:46Z

FloppusMaximus at 21:53, 29 March 2005

2005-03-29T21:53:20Z

New page

[[Category:83Plus:Ports:By_Address]]
== Protected Ports ==
Some of the I/O ports on the 83+ have been "protected" to prevent them from being written accidentally (in addition to preventing user programs from writing to them.)

The following restrictions are believed to apply to all protected ports:

* These ports can only be written to from privileged ROM pages. The privileged ROM pages are two utility code pages and one or two boot code pages. On the normal 83+ the pages are 1Ch, 1Dh, and 1Fh. On the normal 84+ the pages are 3Ch, 3Dh, and 3Fh. On the 83+ SE the pages are 7Ch, 7Dh, and 7Fh. On the 84+ the pages are 6Fh, 7Ch, 7Dh, and 7Fh. (Pages 3C-3E/6C-6E on the 84+, and page 1E/3E/7E, may also qualify, but no code is currently placed on those pages.)

* A specific sequence of instructions must be executed (all of them from a privileged page, with no interruptions) before the port will finally "listen." The sequence is:
nop
nop
im 1
di
out (...),a
: A 'di' often precedes this sequence so that it cannot be broken by an interrupt, and a 'di' often follows it, after which the output value is re-checked, to prevent user programs from sneakily inserting their own output values.

The canonical protected port is, of course, the Flash write-enable port, [[83Plus:Ports:14|port 14]]. Some of the other protected ports also appear to function only when Flash is write-enabled.

@@ Line 3: / Line 3: @@
 Some of the I/O ports on the 83+ have been "protected" to prevent them from being written accidentally (in addition to preventing user programs from writing to them.)  Most of these ports require Flash to be unlocked via port [[83Plus:Ports:14|14]] to respond to write commands.  It was previously thought that all protected ports must be written to with the protected sequence from a protected page, but you may instead use them from anywhere with no sequence if Flash is unlocked.  Port [[83Plus:Ports:14|14]] itself has special requirements that must be met before it will respond:
-* Port [[83Plus:Ports:14|14]] can only be written to from privileged ROM pages. The privileged ROM pages are two utility code pages and one or two boot code pages. On the normal 83+ the pages are 1Ch, 1Dh, and 1Fh. On the normal 84+ the pages are 3Ch, 3Dh, and 3Fh. On the 83+ SE the pages are 7Ch, 7Dh, and 7Fh. On the 84+ SE the pages are 6Fh, 7Ch, 7Dh, and 7Fh.  (Pages 3C-3E/6C-6E on the 84+, and page 1E/3E/7E, may also qualify, but no code is currently placed on those pages.)
+* Port [[83Plus:Ports:14|14]] can only be written to from privileged ROM pages. The privileged ROM pages are two utility code pages and one or two boot code pages. On the normal 83+ the pages are 1Ch, 1Dh, and 1Fh. On the normal 84+ the pages are 3Ch, 3Dh, and 3Fh. On the 83+ SE the pages are 7Ch, 7Dh, and 7Fh. On the 84+ SE the pages are 6Fh, 7Ch, 7Dh, and 7Fh.  (Pages 2C-2E/6C-6E on the 84+, and page 1E/3E/7E, may also qualify, but no code is currently placed on those pages.)
 * A specific sequence of instructions must be executed (all of them from a privileged page, with no interruptions) before the port will finally "listen." The sequence is:

@@ Line 1: / Line 1: @@
 [[Category:83Plus:Ports:By_Address|Protected Ports]]
 == Protected Ports ==
-Some of the I/O ports on the 83+ have been "protected" to prevent them from being written accidentally (in addition to preventing user programs from writing to them.)  Most of these ports require Flash to be unlocked via port [[83Plus:Ports:14|port 14]] to respond to write commands.  It was previously thought that all protected ports must be written to with the protected sequence from a protected page, but you may instead use them from anywhere with no sequence if Flash is unlocked.  Port [[83Plus:Ports:14|port 14]] itself has special requirements that must be met before it will respond:
+Some of the I/O ports on the 83+ have been "protected" to prevent them from being written accidentally (in addition to preventing user programs from writing to them.)  Most of these ports require Flash to be unlocked via port [[83Plus:Ports:14|14]] to respond to write commands.  It was previously thought that all protected ports must be written to with the protected sequence from a protected page, but you may instead use them from anywhere with no sequence if Flash is unlocked.  Port [[83Plus:Ports:14|14]] itself has special requirements that must be met before it will respond:
-* Port [[83Plus:Ports:14|port 14]] can only be written to from privileged ROM pages. The privileged ROM pages are two utility code pages and one or two boot code pages. On the normal 83+ the pages are 1Ch, 1Dh, and 1Fh. On the normal 84+ the pages are 3Ch, 3Dh, and 3Fh. On the 83+ SE the pages are 7Ch, 7Dh, and 7Fh. On the 84+ SE the pages are 6Fh, 7Ch, 7Dh, and 7Fh.  (Pages 3C-3E/6C-6E on the 84+, and page 1E/3E/7E, may also qualify, but no code is currently placed on those pages.)
+* Port [[83Plus:Ports:14|14]] can only be written to from privileged ROM pages. The privileged ROM pages are two utility code pages and one or two boot code pages. On the normal 83+ the pages are 1Ch, 1Dh, and 1Fh. On the normal 84+ the pages are 3Ch, 3Dh, and 3Fh. On the 83+ SE the pages are 7Ch, 7Dh, and 7Fh. On the 84+ SE the pages are 6Fh, 7Ch, 7Dh, and 7Fh.  (Pages 3C-3E/6C-6E on the 84+, and page 1E/3E/7E, may also qualify, but no code is currently placed on those pages.)
 * A specific sequence of instructions must be executed (all of them from a privileged page, with no interruptions) before the port will finally "listen." The sequence is:

@@ Line 1: / Line 1: @@
 [[Category:83Plus:Ports:By_Address|Protected Ports]]
 == Protected Ports ==
-Some of the I/O ports on the 83+ have been "protected" to prevent them from being written accidentally (in addition to preventing user programs from writing to them.)
+Some of the I/O ports on the 83+ have been "protected" to prevent them from being written accidentally (in addition to preventing user programs from writing to them.)  Most of these ports require Flash to be unlocked via port [[83Plus:Ports:14|port 14]] to respond to write commands.  It was previously thought that all protected ports must be written to with the protected sequence from a protected page, but you may instead use them from anywhere with no sequence if Flash is unlocked.  Port [[83Plus:Ports:14|port 14]] itself has special requirements that must be met before it will respond:
-The following restrictions are believed to apply to all protected ports:
+* Port [[83Plus:Ports:14|port 14]] can only be written to from privileged ROM pages. The privileged ROM pages are two utility code pages and one or two boot code pages. On the normal 83+ the pages are 1Ch, 1Dh, and 1Fh. On the normal 84+ the pages are 3Ch, 3Dh, and 3Fh. On the 83+ SE the pages are 7Ch, 7Dh, and 7Fh. On the 84+ SE the pages are 6Fh, 7Ch, 7Dh, and 7Fh.  (Pages 3C-3E/6C-6E on the 84+, and page 1E/3E/7E, may also qualify, but no code is currently placed on those pages.)
-−
-* These ports can only be written to from privileged ROM pages. The privileged ROM pages are two utility code pages and one or two boot code pages. On the normal 83+ the pages are 1Ch, 1Dh, and 1Fh. On the normal 84+ the pages are 3Ch, 3Dh, and 3Fh. On the 83+ SE the pages are 7Ch, 7Dh, and 7Fh. On the 84+ SE the pages are 6Fh, 7Ch, 7Dh, and 7Fh.  (Pages 3C-3E/6C-6E on the 84+, and page 1E/3E/7E, may also qualify, but no code is currently placed on those pages.)
 * A specific sequence of instructions must be executed (all of them from a privileged page, with no interruptions) before the port will finally "listen." The sequence is:
@@ Line 32: / Line 30: @@
   ld d,(hl)
   out (...),a
-: The last works because the opcode for RLC B,(IX+0) is DD CB 00 00, the byte read from (ix) is ED, then the opcode for LD D,(HL) is 56, and the byte read from (hl) is F3.  This could be useful since it allows protected ports to be written without destroying the interrupt mode.
+: The last works because the opcode for RLC B,(IX+0) is DD CB 00 00, the byte read from (ix) is ED, then the opcode for LD D,(HL) is 56, and the byte read from (hl) is F3.  This could be useful since it allows port [[83Plus:Ports:14|port 14]] to be written without destroying the interrupt mode.
-−
-The canonical protected port is, of course, the Flash write-enable port, [[83Plus:Ports:14|port 14]].  Some of the other protected ports also appear to function only when Flash is write-enabled.

@@ Line 1: / Line 1: @@
-[[Category:83Plus:Ports:By_Address|Protected]]
+[[Category:83Plus:Ports:By_Address|Protected Ports]]
 == Protected Ports ==
 Some of the I/O ports on the 83+ have been "protected" to prevent them from being written accidentally (in addition to preventing user programs from writing to them.)