Manual

Technical Description
Sealevel Systems ACB-104 Page 9
DMA Terminal Count
The ACB-104 can be setup to operate using a polling method, interrupts, or system DMA. The most efficient
method is a combination of DMA and interrupts. The ACB-104 has been optimized to generate an interrupt at the
end of a DMA transfer. This will allow DMA initialization and buffer management to take place at interrupt time
and provide a virtually seamless communication channel. If the ‘T’ option on header E5 is selected, an onboard
latch will be set when Terminal Count for the selected DMA channel(s) is reached. This latch will cause an interrupt
to be generated and program execution will be transferred to the application Interrupt Service Routine (ISR). The
DMA Terminal Count Interrupt condition should be reset from the ISR by writing to BASE+5. The value that is
written to this I/O location is irrelevant. If your application or driver is interrupting on multiple conditions, reading
the Status Register located at Base+4 will determine the source of the interrupt (ESCC or DMA Terminal Count
generated). Bit D3 in the Status Port corresponds to a ESCC generated interrupt and bit D5 corresponds to an
interrupt generated by the end of a DMA transfer. Bit D3 can only be reset by polling the ESCC to determine the
interrupt source and required action necessary to reset the interrupt. Please refer to the Software Toolkit and the
85230 Technical Manual for details and examples on interrupt driven and DMA programming examples.
Connector P3 Pin Assignments
RS-232 Signals (At the DB-25)
Signal Name Pin # Mode
GND Ground 7
RD Receive Data 3 Input RS-232
CTS Clear To Send 5 Input RS-232
DSR Data Set Ready 6 Input RS-232
TXC Transmit Clock 15 Input RS-232
RXC Receive Clock 17 Input RS-232
DCD Data Carrier. Detect 8 Output RS-232
TD Transmit Data 2 Output RS-232
RTS Request to Send 4 Output RS-232
TSET Transmit Signal Element Timing 24 Output RS-232
DTR Data Terminal Ready 20 Output RS-232
Note: These assignments meet the EIA/TIA/ANSI-232E DTE Specification
Technical Note: Please terminate any control signals that are not going to be used. The most common way to do this
is connect RTS to CTS and RI. Also, connect DCD to DTR and DSR. Terminating these pins, if not used, will help
insure you get the best performance from your adapter.