Copyright(C) 1994,1995,1996,1997 Terumasa KODAKA, Takeshi KONO
■ Calendar clock
Explanation o The calendar clock is backed up by a battery, so if you turn
off the power, the clock continues to operate.
o Access to the calendar clock should be through the BIOS.
It is best to avoid direct I/O access unless necessary.
o The calendar clock LSI used varies depending on the model.
----------------+----------------------------------------------------------
Calendar clock | Model
----------------+----------------------------------------------------------
μPD1990A | PC-9801 first generation・E・F・M・U・VF・VM2・UV2,PC-98XA,PC-98LT
----------------+----------------------------------------------------------
μPD4990A | PC-9801VX2〜PC-9801NX/C,PC-9821Ce･Af
| Some lots of PC-9801NS/A,NL/R,PC-9821Bf･Cs2･Ce2
----------------+----------------------------------------------------------
μPD4991 | PC-98HA
----------------+----------------------------------------------------------
μPD4993 | PC-9801P・BA2・BS2・BX2,PC-9821Ne・Ap2・As2・Bp・Bs・Be・Ts
| Some lots
----------------+----------------------------------------------------------
μPD4993A | PC-9801P･NS/A･NL/R･BA2･BS2･BX2,PC-9821Ne･Ap2･As2･Bp･Bs･
| Some lots of Be･Bf･Ts･Cs2･Ce2
| PC-9821An･Ap3･As3･Xt･Xa･Xf･Xn･Xp･Xs･Xe･Cf･Cx･Cb･
| Xa16･Xa13･Xa12･Xa10･Xa9･Xa7･Xa7e･Xt16･Xt13･St15･St20･Ra20･
| Xv13･Xb10･Xc10･Xe10･V20･V16･V13･V12･V10･V7･
| Cx2･Cb2･Cx3･Cb3･
| Np･Ns･Ne2･Nd･Es･Ne3･Nd2･Nf･Nm･Ld･Lt･Ld2･Nx･Na12･Na9･Na7･
| Nb7･La10･La7
| PC-9821BA3･BX3･BX4
----------------+----------------------------------------------------------
None | DB-P1
----------------+----------------------------------------------------------
u On a device equipped with μPD4993, if the date changes while the power is
off, the year will not be updated or the setting for February 29th will not
be performed automatically in a leap year.
u In order to correct the above-mentioned problem in models equipped with
μPD4993, NEC has released a patch for IO.SYS in MS-DOS 5.0A and earlier
versions. It is also fixed in MS-DOS 6.2 and later and Windows 95 by
including BCKWHEAT.SYS.
o For models equipped with a calendar clock interrupt, it is possible to
generate an INT 17h (IRQ15) interrupt to the CPU using the μPD4993A's pulse
output.
o For models equipped with calendar clock interrupts, it is possible to obtain
the time in 1/100 second units using DOS functions by installing the device
driver HRTIMER.SYS in the MS-DOS environment.
Related I/O 000Ah bit 7
INT 17h
I/O 0020h
Name Calendar clock
Applicable to All models (excluding PC-98HA, DB-P1)
Chip μPD1990A, μPD4990A, μPD4993, μPD4993A
Function ------------+-------+-----+-----------------------------------------------
I/O address | width | R/W | content
------------+-------+-----+-----------------------------------------------
0020h | BYTE | R | μPD1990A and μPD4990A are not used.
| | | For machines equipped with μPD4993(A), it is used
| | | when I/O 0022h bit 4=1. details unknown.
0020h | BYTE | W | Set register
| | | bit 7,6: 00b
| | | bit 5: Data input
| | | bit 4: Clock
| | | bit 3: Strobe
| | | bit 2~0: C2~C0 command code
| | | 111b=Extended mode command (*1)
| | | 110b=TP=64Hz set (*1)
| | | 101b=TP=256Hz set (*1)
| | | 100b=TP=2048Hz set (*1)
| | | 011b=Time lead
| | | 010b=Time set & counter hold
| | | 001b=Register shift
| | | 000b=Register hold
| | | *1: μPD1990A is not supported
------------+-------+-----+-----------------------------------------------
Explanation o The data out terminal of the calendar clock IC is connected to system port B0.
o Since the μPD1990A does not have a function to handle the year, the year value
is stored in memory switch 8 (A000:3FFEh, E000:3FFEh) on devices equipped with
the μPD1990A. For this reason, processing for new years and leap years is not
performed automatically.
Related I/O 0033h bit0
I/O 8E1Eh ■ [PC-9801P]
A000:3FFEh ■ [PC-9801 first generation・E・F・M・U・VM2・VF・UV2]
INT 1Ch - Function 00h
INT 1Ch - Function 01h
I/O 0022h
Name Calendar clock control
Undocumented
Target μPD4993(A) equipped machine
Chip μPD4993(A)
Function ------------+-------+-----+-----------------------------------------------
I/O address | width | R/W | content
------------+-------+-----+-----------------------------------------------
0022h | BYTE | R/W | bit 4: μPD4993(A) mode setting
| | | 1=μPD4993 extended mode
| | | 0=μPD4990 compatibility mode
------------+-------+-----+-----------------------------------------------
Explanation o It is thought to be used for control to enable/disable the extended functions
of μPD4993(A). If bit 4=1, the calendar clock LSI cannot be accessed using
normal methods.
Related I/O 0020h
I/O 0022h,0023h
Name Calendar clock
Undocumented
Target PC-98HA
Chip μPD4991
Function ------------+-------+-----+-----------------------------------------------
I/O address | width | R/W | content
------------+-------+-----+-----------------------------------------------
0022h | BYTE | W | Addressing
| | | bit 7~4: Unused (specify 0)
| | | bit 3~0: A3~A0 address
0023h | BYTE | R/W | Data input/output
| | | bits 7 to 4: Unused (specify 0 when writing)
| | | bit 3～0: D3～D0 input/output data
------------+-------+-----+-----------------------------------------------
Explanation o The PC-98HA uses μPD4991 to implement the alarm function.
u The μPD4991 performs I/O with the CPU using 4-bit address lines and 4-bit
data lines. In the PC-98HA, the circuit is configured so that after
outputting an address to I/O 0022h, data is input/output using I/O 0023h.
o For details on μPD4991, refer to the manufacturer's data sheet.
Related INT 1Ch - Function 00h
INT 1Ch - Function 01h
INT 1Ch - Function 07h
INT 1Ch - Function 08h
INT 1Ch - Function 09h
I/O A98Eh,B98Eh
Name Calendar clock
Undocumented
Target PC-9801P
Chip μPD4991
Function ------------+-------+-----+-----------------------------------------------
I/O address | width | R/W | content
------------+-------+-----+-----------------------------------------------
A98Eh | BYTE | W | Addressing
| | | bit 7~4: Unused (specify 0)
| | | bit 3~0: A3~A0 address
B98Eh | BYTE | R/W | Data input/output
| | | bits 7 to 4: Unused (specify 0 when writing)
| | | bit 3～0: D3～D0 input/output data
------------+-------+-----+-----------------------------------------------
Explanation o The PC-9801P is designed to be able to be equipped with an additional
μPD4991 in order to realize the wake-up function (however, in the actually
shipped product, the printed pattern remains on the board, but the μPD4991
is (Not implemented. BIOS support routines remain, but this feature does
not work due to the lack of hardware).
u The μPD4991 performs I/O with the CPU using 4-bit address lines and 4-bit
data lines. In the PC-9801P, the circuit is configured so that after
outputting an address to I/O A98Eh, data is input/output using I/O B98Eh.
o For details on μPD4991, refer to the manufacturer's data sheet.
Related INT 1Fh - Function 9A12~9A16h
I/O 0128h
Target Models equipped with calendar clock interrupts
Function [READ/WRITE]
bit 7～0: Details unknown
80h=
81h=
Description o Controls the pulse output interrupt of the calendar clock IC.
o Lower interrupt requests by reading.
o Details unknown
Related INT 17h
INT 1Ch - Function 80h,81h
INT 1Fh - Function 8Fh
I/O 000Ah bit 7
0000:04F1~04F3h