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  1. CAPS LOCK Q. Previously an error in key matrix decode table caused a lowercase 'Q' to be passed when the keyboard is in CAPS LOCK mode. The table has been corrected by substituting the correct value for upper-case 'Q'.
  2. FUNCTION KEYs. Previously the function key handler, part of the SCNKEY routine at CKIT2, failed to detect a function key string pending. This has been corrected via patch routine, which will ignore new function key depressions until the string in prograss has been output (i.e., KYNDX = 0). Also, DOPFKEY now exits via SCNRTS, instead of simply RTSing.
  3. IOINIT system initialization. Previously the RS-232 pseudo-6551 registers were not initialized because these values are expected to be given by the user whenever RS-232 channels are OPENed. Apparently many C64 users have taken advantage of the fact the C64 'happened' to clear these locations an fail to specify critical parameters. These RS-232 registers are now initialized to default to: no parity, full duplex, 3-line, 1-stop bit, 8-bit words and 300 baud, via a patch subroutine.
  4. IOINIT PAL system initialization. Adjustements have been made to the 8563 initialization values fro PAL systems. The PAL horizontal total (register 0) changes from $7E to $7F. The PAL vertical total (register 4) changes from $27 to $26. These changes sift the cycle time from 20.320us to 20.032us. The patch required a patch subroutine as well as a change to VDCTBL.
  5. BASIN system call. Previosly attempting input from a logical channel to the screen (e.g., via INPUT#) resulted line too long errors. This has been corrected utilizing a subroutine patch to preserve bit-7 of CRSW, which serves as a flag to the Editor that a (pseudo) end-of-line has been reached. Also, TBLX is copied to LINTMP to correctly locate the current cursor line for the Editor. Please note that switching between the 40 and 80-column text screens, opening and closing windows, or clearing text screens can confuse logical screen channels. The Editor variable LINTMP ($A30) is a global, not local, variable as it should have been. Users can POKE LINTMP with the logical screen line number before INPUT#'s as a work-around.
  6. OPEN RS-232 system call. Previously it was possible to receive a carry-set status, normally indicating an error, when no error existed after OPENing an RS-232 channel. This has been corrected totally in-line by a modification to the code which checks for the proper X-line hardware states.
  7. LOAD system call. Previously the normal (a.k.a. SLOW) load mechanism old not preserve the starting address of any LOADs, which made the BASIC 'BOOT "file"' command form malfunction unpredictably. This is apparent only when used with 1541 drives. This has been corrected via a patch subroutine, which saves the starting address of all LOADed files at SAL and SAH, the same place the fast (a.k.a. BURST) load mechanism does.
  8. DMA system call. Previosly the Kernel forced the I/O block into the user's memory configuration at all times, which is no longer necessary and, in fact, seriously limits the functionality of the RAM expansion cartridge. This has been corrected by a ROM patch routine, which affects all Kernel DMA system calls as well as the BASIC FETCH, STASH, and SWAP commands. Also, previously it was possible for an IRQ to occur between the 'arm DMA' and 'trigger DMA' sequences, resulting in a DMA orperation with the system configuration in context regardless of desired configuration. This has been corrected by adding 'PHP/SEI...PLP' instructions around the JSR to DMA RAM code at $3F0. Applications using the DMA RAM code at $3F0 should do likewise. Finally, in this patch changes were made to enable DMA operations to all RAM banks by correctly using The VIC bank pointer found in the MMU RAM configuration register ($D506, VA16=bit-6 and VA17=bit-7). Applications using the Kernel routine at $FF50 will inherit these changes automatically. Please note that NMI interrupts can screw-up DMA operations, as they cannot be masked.

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This page has been created by Sami Rautiainen.
Read the small print. Last updated April 06, 2006.