Datum bc630AT, Руководство пользователя

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CHAPTER THREE
3-12 bc630AT Real Time Clock Module Datum Inc
3.4.2 REQUESTING AND READING TIME
To request time from the bc630AT over the XT/AT bus, issue the 'Time Request' command by writing
80H to the Command Register (offset 0EH). This action causes the bc630AT to freeze the time and
transfer it to the Data Transfer Address Space (offset 00H - 06H). Following the transfer of time, the
bc630AT will write the ready flag value of 00H to the Command Register indicating the requested time
is ready to be read by the XT/AT bus and the bc630AT is ready to receive another command.
The bc630AT requires approximately 150
:
secs to load the Data Transfer Address Space with the time
in response to a Time Request. The time, however, is frozen at the instant the 'Time Request' is issued.
3.4.3 EXTERNAL EVENT CAPTURE
The bc630AT has the ability to capture time in response to an external event. Use bits 0 and 1 in the
Masks Register to enable the external event function and to select the active edge for capture. When
the bc630AT detects the appropriate edge of the event signal it will:
•
Freeze time and load it into an internal buffer.
•
Set the Event bit in the Status register.
•
Generate an interrupt to the host PC (if selected as the interrupt source in the Masks
register) by writing the value 40H to the Interrupt register. (See section 3.1.4.)
The Event Time is transferred to the Data Transfer Address Space by issuing the 'Request Event Time'
command 81H. Following the Event Time transfer, the bc630AT will write the ready flag value of 01H
to the Command Register indicating the requested time is ready to be read by the XT/AT bus, and the
bc630AT is ready to receive another command. At this point the event capture circuitry is disabled.
To capture another edge with the parameters defined in the Masks register issue a 'Clear Event
Capture' command. This reactivates the event capture circuitry.
The bc630AT requires approximately 150 : secs to load the Event Time to the Data Transfer Address
Space in response to 'Request Event Time' command. The time, however, is frozen at the instant that
the External Event Input is activated.
3.4.4 RATE PROGRAMMABLE HEARTBEAT PULSES
It is often useful to generate a periodic pulse/interrupt (heartbeat) which is synchronized to the time
source signal. The bc630AT has the ability to generate heartbeat pulses/interrupts between a 1-2000
Hz rate. The Masks Register bit 4 enables the heartbeat, and the registers HBRATE0 and HBRATE1
determine the rate of the pulses/interrupts (in pulses per second). Following a change to the Heartbeat
Rate registers the user must 'Initialize' the bc630AT or issue the 'Synchronize Heartbeats' command.
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