diff options
Diffstat (limited to 'src/devices/cpu/m6502/m6500_1.cpp')
-rw-r--r-- | src/devices/cpu/m6502/m6500_1.cpp | 22 |
1 files changed, 11 insertions, 11 deletions
diff --git a/src/devices/cpu/m6502/m6500_1.cpp b/src/devices/cpu/m6502/m6500_1.cpp index 6ba2f9c3919..8aa30f08c89 100644 --- a/src/devices/cpu/m6502/m6500_1.cpp +++ b/src/devices/cpu/m6502/m6500_1.cpp @@ -12,10 +12,10 @@ * Sixteen-bit programmable counter/latch The onboad clock generator has mask options for an external crystal - (2MHz to 6MHz) an external TTL-compatible clock with a 300Ω pull-up + (2MHz to 6MHz), an external TTL-compatible clock with a 300Ω pull-up resistor (2MHz to 6MHz), or an RC oscillator with an external 47kΩ resistor and internal capacitor (nominally 2MHz). The clock is - divided by two to generate the two-phase CPU code clock. + divided by two to generate the two-phase CPU core clock. There is no on-board power-on reset generator. The /RES pin must be held low (asserted) for at least eight phase 2 clock cycles after @@ -45,7 +45,7 @@ on the CNTR pin in event counter mode is half the phase 2 clock rate. This suggests that an internal flag is set when a rasing edge is detected on CNTR and reset when the counter is synchronously - decremented. This is not emulated - for simplicity the counter is + decremented. This is not emulated - for simplicity, the counter is asynchronously decremented on detecting a rising edge on CNTR. The CNTR pin has an active low driver and internal passive pull-up. @@ -59,14 +59,14 @@ is unknown what other differences these devices have. TODO: - - For some reason most if not all Amiga MCU programs accesses arbitrary - zero page 0x90-0xff with a back-to-back cmp($00, x) opcode at - PC=c06-c08 with the actual result discarded. X can be any value in - the 0x90-0xff range, depending on the last user keypress row source - e.g. 0xdf-0xe0 for 'A', 0xef-0xf0 for 'Q', 0xfb-0xfc for function - keys. - This can be extremely verbose in the logging facility so we currently - nop it out for the time being. + - For some reason most if not all Amiga MCU programs access + arbitrary zero page 0x90-0xff with a back-to-back cmp($00, x) + opcode at PC=c06-c08 with the actual result discarded. X can be + any value in the 0x90-0xff range, depending on the last user + keypress row source e.g. 0xdf-0xe0 for 'A', 0xef-0xf0 for 'Q', + 0xfb-0xfc for function keys. + This can be extremely verbose in the logging facility so we nop it + out for the time being. ***************************************************************************/ |