AT REAL TIME CLOCK


The following information is provided for use "as-is" and is not guaranteed
to be completely correct. I have made ever attempt to check for correctness.
If you should have any corrections let me know.

Thank You
James McDaniel
CIS 74365,1716


I/O ports 70 and 71 HEX. Send address to I/O port 70 and read data
from I/O port 71. See data sheet on MC14818 for more info on commands
and there use. A breakdown of memory locations and there use follows.


AT REAL TIME CLOCK RAM CONFIGURATION USAGE

---------------------------------------------------------------------------
ADDRESS FUNCTION COMMENTS
---------------------------------------------------------------------------
0H SECONDS
1H SECOND ALARM
2H MINUTES
3H MINUTE ALARM
4H HOURS
5H HOUR ALARM
6H DAY OF WEEK
7H DAY OF MONTH
8H MONTH
9H YEAR
0AH STATUS REGISTER A SEE AT RTC STATUS REGISTER A
0BH STSTUS REGISTER B SEE AT RTC STATUS REGISTER B
0CH STATUS REGISTER C SEE AT RTC STATUS REGISTER C
0DH STATUS REGISTER D SEE AT RTC STATUS REGISTER D
0EH DIAGNOSTIC STATUS BYTE SEE AT RTC DIAGNOSTIC STATUS BYTE
0FH SHUTDOWN STATUS BYTE DEFINED BY POWER ON DIAGNOSTICS
10H DISK DRIVE TYPE BYTE SEE AT RTC DISKETTE DRIVE TYPE BYTE
11H RESERVED
12H FIXED DRIVE TYPE SEE AT RTC FIXED DRIVE TYPE BYTE
13H RESERVED
14H EQUIPMENT BYTE SEE AT RTC EQUIPMENT BYTE
15H LOW BASE MEMORY BYTE
16H HIGH BASE MEMORY BYTE 100H=256K,200H=512K,280=640K
17H LOW EXPANSION MEMORY BYTE
18H HIGH EXPANSION MEMORY BYTE 200H=512K,400H=1024K,600-3C00H=TO 15360K
19H DRIVE C EXTENDED BYTE SEE AT FIXED DISK DRIVE TYPES (TO 0EH)
1AH DRIVE D EXTENDED BYTE SEE AT FIXED DISK DRIVE TYPES (TO 0EH)
1BH-2DH RESERVED
2EH-2FH CHECKSUM SIMPLE ADD OF DATA @ ADDRESSES 10-2DH
30H LOW EXPANSION MEMORY BYTE
31H HIGH EXPANSION MEMORY BYTE 200H=512K,400H=1024K,600-3C00H=TO 15360K
32H DATE CENTURY BYTE BCD VALUE FOR CENTURY
33H INFORMATION FLAGS (BIT 7 SET = TOP 128K INSTALLED - CONT.
34H-3FH RESERVED CONT. BIT 6 SET = FIRST USER MESSAGE)








AT REAL TIME CLOCK STATUS REGISTER A

---------------------------------------------------------------------------
7 6 5 4 3 2 1 0 FUNCTION ALLOWABLE VALUES
---------------------------------------------------------------------------
X UPDATE IN PROGRESS 1=DATE/TIME BEING UPDATED 0=NOT
X X X 22 STAGE DIVIDER DEFAULT=010, 32.768 KHZ TIME BASE
X X X X RATE SELECTION DEFAULT=0110, 1.024 KHZ FREQUENCY





AT REAL TIME CLOCK STATUS REGISTERS B

-------------------------------------------------------------------------
7 6 5 4 3 2 1 0 NAME ALLOWABLE VALUES
--------------------------------------------------------------------------
X SET, 1 PER SECOND 0=UPDATE NORMALLY, 1=ABORT UPDATE
X PERIODIC INT ENABLE 0=DISABLE INT (DEFAULT), 1=ENABLED
X ALARM INT ENABLE 0=DISABLED (DEFAULT), 1=ENABLED
X UPDATE END INT ENA. 0=DISABLED (DEFAULT), 1=ENABLED
X SQUARE WAVE ENABLE 0=DIS (DEF), 1=ENA, PER REG A 0-3
X DATE MODE 0=BCD (DEFAULT), 1=BINARY
X 24/12 MODE 0=12 HOUR, 1=24 HOUR FORMAT (DEFAULT)
X DAYLIGHT SAVING ENA 0=DISABLED (DEFAULT), 1=ENABLED


AT REAL TIME CLOCK STATUS REGISTER C

-------------------------------------------------------------------------
7 6 5 4 3 2 1 0 NAME ALLOWABLE VALUES
-------------------------------------------------------------------------
X IRQF FLAG READ ONLY
X PF FLAG READ ONLY
X AF FLAG READ ONLY
X UF FLAG READ ONLY
X X X X RESERVED SHOULD ALWAYS BE ZERO


AT REAL TIME CLOCK STATUS REGISTER D

--------------------------------------------------------------------------
7 6 5 4 3 2 1 0 NAME ALLOWABLE VALUES
--------------------------------------------------------------------------
X VALID RAM BIT 0=BATT DEAD,RAM INVALID, 1=BATT GOOD
X X X X X X X RESERVED SHOULD ALWAYS BE ZERO


AT REAL TIME CLOCK DIAGNOSTICS BYTE

------------------------------------------------------------------------
7 6 5 4 3 2 1 0 NAME ALLOWABLE VALUES
------------------------------------------------------------------------
X POWER STAT OF RTC 1=CHIP HAS LOST POWER, 0=NOT
X CHECKSUM STATUS 0=CHECKSUM OK, 1=NOT OK
X CONFIGURATION INFO 0=VALID INFO, 1=NOT VALID
X MEMORY SIZE COMPARE 0=SAME SIZE, 1=NOT SAME SIZE
X FIXED DISK STATUS 0=OK, 1=DRIVE OR ADAPTER FAILED
X TIME STATUS 0=TIME IS OK, 1=TIME NOT OK
X X RESERVED







AT REAL TIME CLOCK DRIVE TYPE BYTE

-------------------------------------------------------------------------
7 6 5 4 3 2 1 0 FUNCTION ALLOWABLE VALUES
-------------------------------------------------------------------------
X X X X TYPE OF FIRST DRIVE 0000=NO DRIVE, 0001=360K 5.25"
0010=1.2M 5.25" 0011=720K 3.5"
0100=1.44M 3.5"

X X X X TYPE OF SECOND DRIVE




AT REAL TIME CLOCK FIXED DRIVE TYPES

----------------------------------------------------------------------------
7 6 5 4 3 2 1 0 NAME ALLOWABLE VALUES
----------------------------------------------------------------------------
X X X X FIXED DISK C TYPE 0000=NO DRIVE 1H TO 0EH SEE CHART
X X X X FIXED DISK D TYPE 0000=NO DRIVE 1H TO 0EH SEE CHART

IF BYTE= 0FH THEN SEE EXTENDED BYTE FOR DRIVE TYPE



AT REAL TIME CLOCK EQUIPMENT BYTE

-----------------------------------------------------------------------------
7 6 5 4 3 2 1 0 NAME ALLOWABLE VALUES
-----------------------------------------------------------------------------
X X NUMBER OF DISK DRIVES 00=1,01=2, OTHER VALUES RESERVED
X X PRIMARY DISPLAY TYPE 00=DISPLAY HAS BIOS,01=40 COL CGA
10=80 COL CGA, 11=MDA
X X NOT USED
X MATH COPROCESSOR 0=NOT INSTALLED, 1=INSTALLED
X DISK DRIVES AVAILABLE 0=NO DRIVES, 1=DISK DRIVES AVAILABLE


AT REAL TIME CLOCK DRIVE C AND D EXTENDED DRIVE TYPE BYTES

-----------------------------------------------------------------------------
7 6 5 4 3 2 1 0 NAME ALLOWABLE VALUES
-----------------------------------------------------------------------------
X X X X X X X X DRIVE C TYPE BYTE SEE NEXT CHART FOR TYPES
X X X X X X X X DRIVE D TYPE BYTE SEE NEXT CHART FOR TYPES

IF FIXED DRIVE 4 BITS FOR C IS 0-0EH IGNOR EXTENDED C
IF FIXED DRIVE 4 BITS FOR D IS 0-0EH IGNOR EXTENDED D
















AT HARD DISK TYPES

+--------------------------------------------------------+
| | | | | | | |
| DISK | CYLINDER | TOTAL | PRE- | LAND | SECTORS | SIZE |
| TYPE | COUNT | HEADS | COMP | ZONE | PER/TRK | MB |
|------+----------+-------+------+------+---------+------|
| 1 | 306 | 4 | 128 | 305 | 17 | 10.1 |
|------+----------+-------+------+------+---------+------|
| 2 | 615 | 4 | 300 | 615 | 17 | 20.4 |
|------+----------+-------+------+------+---------+------|
| 3 | 615 | 6 | 300 | 615 | 17 | 30.6 |
|------+----------+-------+------+------+---------+------|
| 4 | 940 | 8 | 512 | 940 | 17 | 62.4 |
|------+----------+-------+------+------+---------+------|
| 5 | 940 | 6 | 512 | 940 | 17 | 46.8 |
|------+----------+-------+------+------+---------+------|
| 6 | 615 | 4 | NONE | 615 | 17 | 20.4 |
|------+----------+-------+------+------+---------+------|
| 7 | 462 | 8 | 256 | 511 | 17 | 30.6 |
|------+----------+-------+------+------+---------+------|
| 8 | 733 | 5 | NONE | 733 | 17 | 30.4 |
|------+----------+-------+------+------+---------+------|
| 9 | 900 | 15 | NONE | 901 | 17 |112.0 |
|------+----------+-------+------+------+---------+------|
| 10 | 820 | 3 | NONE | 820 | 17 | 20.4 |
|------+----------+-------+------+------+---------+------|
| 11 | 855 | 5 | NONE | 855 | 17 | 35.4 |
|------+----------+-------+------+------+---------+------|
| 12 | 855 | 7 | NONE | 855 | 17 | 49.6 |
|------+----------+-------+------+------+---------+------|
| 13 | 306 | 8 | 128 | 319 | 17 | 20.3 |
|------+----------+-------+------+------+---------+------|
| 14 | 733 | 7 | NONE | 733 | 17 | 42.5 |
|------+----------+-------+------+------+---------+------|
| 16 | 612 | 4 | 0 | 663 | 17 | 20.5 |
|------+----------+-------+------+------+---------+------|
| 17 | 977 | 5 | 300 | 977 | 17 | 40.5 |
|------+----------+-------+------+------+---------+------|
| 18 | 977 | 7 | NONE | 977 | 17 | 56.7 |
|------+----------+-------+------+------+---------+------|
| 19 | 1024 | 7 | 512 | 1023 | 17 | 59.5 |
|------+----------+-------+------+------+---------+------|
| 20 | 733 | 5 | 300 | 732 | 17 | 30.4 |
|------+----------+-------+------+------+---------+------|
| 21 | 733 | 7 | 300 | 732 | 17 | 42.5 |
|------+----------+-------+------+------+---------+------|
| 22 | 733 | 5 | 300 | 733 | 17 | 30.4 |
|------+----------+-------+------+------+---------+------|
| 23 | 306 | 4 | 0 | 336 | 17 | 10.1 |
|------+----------+-------+------+------+---------+------|
| 25 | 615 | 4 | 0 | 615 | 17 | 20.4 |
|------+----------+-------+------+------+---------+------|
| 26 | 1024 | 4 | NONE | 1023 | 17 | 34.0 |
+--------------------------------------------------------+











AT HARD DISK TYPES

+--------------------------------------------------------+
| | | | | | | |
| DISK | CYLINDER | TOTAL | PRE- | LAND | SECTORS | SIZE |
| TYPE | COUNT | HEADS | COMP | ZONE | PER/TRK | MB |
|------+----------+-------+------+------+---------+------|
| 27 | 1024 | 5 | NONE | 1023 | 17 | 42.5 |
|------+----------+-------+------+------+---------+------|
| 28 | 1024 | 8 | NONE | 1023 | 17 | 68.0 |
|------+----------+-------+------+------+---------+------|
| 29 | 512 | 8 | 256 | 512 | 17 | 34.0 |
|------+----------+-------+------+------+---------+------|
| 30 | 615 | 2 | 615 | 615 | 17 | 10.2 |
|------+----------+-------+------+------+---------+------|
| 31 | 989 | 5 | 0 | 989 | 17 | 41.0 |
|------+----------+-------+------+------+---------+------|
| 32 | 1020 | 15 | NONE | 1024 | 17 |127.0 |
|------+----------+-------+------+------+---------+------|
| 35 | 1024 | 9 | 1024 | 1024 | 17 | 76.5 |
|------+----------+-------+------+------+---------+------|
| 36 | 1024 | 5 | 512 | 1024 | 17 | 42.5 |
|------+----------+-------+------+------+---------+------|
| 37 | 830 | 10 | NONE | 830 | 17 | 68.8 |
|------+----------+-------+------+------+---------+------|
| 38 | 823 | 10 | 256 | 824 | 17 | 68.3 |
|------+----------+-------+------+------+---------+------|
| 39 | 615 | 4 | 128 | 664 | 17 | 20.4 |
|------+----------+-------+------+------+---------+------|
| 40 | 615 | 8 | 128 | 664 | 17 | 40.8 |
|------+----------+-------+------+------+---------+------|
| 41 | 917 | 15 | NONE | 918 | 17 |114.1 |
|------+----------+-------+------+------+---------+------|
| 42 | 1023 | 15 | NONE | 1024 | 17 |127.3 |
|------+----------+-------+------+------+---------+------|
| 43 | 823 | 10 | 512 | 823 | 17 | 68.3 |
|------+----------+-------+------+------+---------+------|
| 44 | 820 | 6 | NONE | 820 | 17 | 40.8 |
|------+----------+-------+------+------+---------+------|
| 45 | 1024 | 8 | NONE | 1024 | 17 | 68.0 |
|------+----------+-------+------+------+---------+------|
| 46 | 925 | 9 | NONE | 925 | 17 | 69.1 |
|------+----------+-------+------+------+---------+------|
| 47 | 699 | 7 | 256 | 700 | 17 | 40.6 |
+--------------------------------------------------------+