0070-007F ---- CMOS RAM/RTC (Real Time Clock  MC146818)


0070   w   CMOS RAM index register port (ISA, EISA)
        bit 7   = 1  NMI disabled
            = 0  NMI enabled
        bit 6-0      CMOS RAM index (64 bytes, sometimes 128 bytes)

       any write to 0070 should be followed by an action to 0071
       or the RTC wil be left in an unknown state.

0071   r/w CMOS RAM data port (ISA, EISA)
       RTC registers:
       00    current second in BCD
       01    alarm second   in BCD
       02    current minute in BCD
       03    alarm minute   in BCD
       04    current hour in BCD
       05    alarm hour   in BCD
       06    day of week  in BCD
       07    day of month in BCD
       08    month in BCD
       09    year  in BCD (00-99)
       0A    status register A
              bit 7 = 1  update in progress
              bit 6-4 divider that identifies the time-based
               frequency
              bit 3-0 rate selection output  frequency and int. rate
       0B    status register B
              bit 7 = 0  run
                = 1  halt
              bit 6 = 1  enable periodic interrupt
              bit 5 = 1  enable alarm interrupt
              bit 4 = 1  enable update-ended interrupt
              bit 3 = 1  enable square wave interrupt
              bit 2 = 1  calendar is in binary format
                = 0  calendar is in BCD format
              bit 1 = 1  24-hour mode
                = 0  12-hour mode
              bit 0 = 1  enable daylight savings time. only in USA.
                 useless in Europe. Some DOS versions clear
                 this bit when you use the DAT/TIME command.
       0C    status register C
              bit 7 =    interrupt request flag
              bit 6 =    peridoc interrupt flag
              bit 5 =    alarm interrupt flag
              bit 4 =    update interrupt flag
              bit 3-0    reserved
       0D    status register D
              bit 7 = 1  Real-Time Clock has power
              bit 6-0    reserved
       0E    diagnostics status byte
              bit 7 = 0  RTC lost power
              bit 6 = 1  CMOS RAM checksum bad
              bit 5 = 1  invalid configuration information at POST
              bit 4 = 1  memory size error at POST
              bit 3 = 1  fixed disk/adapter failed initialization
              bit 2 = 1  CMOS RAM time found invalid
              bit 1 = 1  adapters do not match configuration (EISA)
              bit 0 = 1  time out reading an adapter ID (EISA)
       0F    shutdown status byte
              00 = normal execution of POST
              01 = chip set initialization for real mode reentry
              04 = jump to bootstrap code
              05 = issue an EOI an JMP to Dword ptr at 40:67
              06 = JMP to Dword ptrv at 40:67 without EOI
              07 = return to INT15/87 (block move)
              08 = return to POST memory test
              09 = return to INT15/87 (block move)
              0A = JMP to Dword ptr at 40:67 without EOI
              0B = return IRETS through 40:67
       10    diskette drive type for A: and B:
              bit 7-4  drive type of drive 0
              bit 3-0  drive type of drive 1
                  = 0000      no drive
                  = 0001      360K
                  = 0010      1M2
                  = 0011      720K
                  = 0100      1M44
                  = 0101-1111 reserved
       11    reserved / AMI Extended CMOS setup (AMI Hi-Flex BIOS)
              bit 7   = 1     Typematic Rate Programming
              bit 6-5 = 00    Typematic Rate Delay 250 mSec
              bit 4-0 = 00011 Typematic Rate 21.8 Chars/Sec
       12    fixed disk drive type for drive 0 and drive 1
              bit 7-4  drive type of drive 0
              bit 3-0  drive type of drive 1
               if either of the nibbles equals 0F, then bytes
               19 an 1A are valid
       13    reserved / AMI Extended CMOS setup (AMI Hi-Flex BIOS)
              bit 7 = 1  Mouse Support Option
              bit 6 = 1  Above 1 MB Memory Test disable
              bit 5 = 1  Memory Test Tick Sound disable
              bit 4 = 1  Memory Parity Error Check enable
              bit 3 = 1  Hit <ESC> Message Display disabled
              bit 2 = 1  Hard Disk Type 47 Data Area at address 0:300
              bit 1 = 1  Wait For <F1> If Any Error enabled
              bit 0 = 1  System Boot Up Num Lock is On
       14    equipment byte
              bit 7-6   diskette drives installed
                  = 00  1 drive installed
                  = 01  2 drives installed
                  = 10  reserved
                  = 11  reserved
              bit 5-4   primary display
                  = 00  adapter card with option ROM
                  = 01  40*25 color
                  = 10  80*25 color
                  = 11  monochrome
              bit 3-2   reserved
              bit 1   = 1  coprocessor installed (non-Weitek)
              bit 0        diskette drive avaliable for boot
       15    LSB of systemn base memory in Kb
       16    MSB of systemn base memory in Kb
       17    LSB of total extended memory in Kb
       18    MSB of total extended memory in Kb
       19    drive C extension byte
       1A    drive D extension byte
       1B-27 reserved
       1B/1C word to 82335 RC1 roll compare register at [24]
           (Phoenix)
       1D/1E word to 82335 RC2 roll compare register at [26]
           (Phoenix)
       28    HP-Vectra checksum over 29-2D
       29-2D reserved
       29/2A word to Intel 82335 CC0 compare register at
           [28](Phoenix)
       2B/2C word send to 82335 CC1 compare register at [2A]
           (Phoenix)
       2D    AMI Extended CMOS setup (AMI Hi-Flex BIOS)
             (Phoenix BIOS checks for the values AA or CC)
              bit 7 = 1  Weitek Processor Absent
              bit 6 = 1  Floppy Drive Seek At Boot disabled
              bit 5 = 1  System Boot Up Sequence  C:, A:
              bit 4 = 1  System Boot Up Speed is high
              bit 3 = 1  Cache Memory enabled
              bit 2 = 1  Internal Cache Memory  <1>
              bit 1-0    reserved
       2E    CMOS MSB checksum over 10-2D
       2F    CMOS LSB checksum over 10-2D
       30    LSB of extended memory found above 1Mb at POST
       31    MSB of extended memory found above 1Mb at POST
       32    date century in BCD
       33    information flags
              bit4 = bit4 from CPU register CR0   (Phoenix)
                 this bit is only known as INTEL RESERVED
       34-3F reserved
       34     bit4 bit5 (Phoenix BIOS)
       3D/3E word to 82335 MCR memory config register at
           [22](Phoenix)
       3D     bit3  base memsize 512/640  (Phoenix)
       3E     bit7 = 1  relocate enable       (Phoenix)
              bit1 = 1  shadow video enable   (Phoenix)
              bit0 = 1  shadow BIOS enable    (Phoenix)


       User Definable Drive Parameters are also stored in CMOS RAM:

       AMI (386sx BIOS 1989) first user definable drive (type 47)
        1B  L cylinders
        1C  H cylinders
        1D  heads
        1E  L Write Precompensation Cylinder
        1F  H Write Precompensation Cylinder
        20  ??
        21  L cylinders parking zone
        22  H cylinders parking zone
        23  sectors

       AMI (386sx BIOS 1989) second user definable drive (type 48)
        24  L cylinders
        25  H cylinders
        26  heads
        27  L Write Precompensation Cylinder
        28  H Write Precompensation Cylinder
        29  ??
        2A  L cylinders parking zone
        2B  H cylinders parking zone
        2C  sectors

       Phoenix (386BIOS v1.10.03 1988) 1st user definable drv (type48)
        20  L cylinders
        21  H cylinders
        22  heads
        23  L Write Precompensation Cylinder
        24  H Write Precompensation Cylinder
        25  L cylinders parking zone
        26  H cylinders parking zone
        27  sectors

       Phoenix (386BIOS v1.10.03 1988) 2nd user definable drv (type49)
       (when PS/2-style password option is not used)
        35  L cylinders
        36  H cylinders
        37  heads
        38  L Write Precompensation Cylinder
        39  H Write Precompensation Cylinder
        3A  L cylinders parking zone
        3B  H cylinders parking zone
        3C  sectors

0078       HP-Vectra  Hard Reset: NMI enable/disable
        bit 7 = 0  disable & clear hard reset from HP-HIL controller
              = 1  enable hard reset from HP-HIL controller chip
        bit 6-0    reserved