Instruction manual

9.5.2.9 ISDN DMA
ISDN has both a receive and a transmit address pointer and address buffer
pointer. These prevent DMA stalling, if software could not load a new address in
a timely manner.
If an ISDN transmit DMA pointer crosses a page boundary, the transmit buffer
pointer is loaded into the transmit pointer, and an interrupt is set. This directs
software to reload the buffer pointer. If the buffer pointer is empty, the DMA is
turned off because an invalid address was loaded into the pointer, and another
interrupt is set signaling overflow. A buffer pointer may be empty because it was
never written to or has not been written to since the last page crossing.
The receive side is identical to the transmit side. See Section 7.3.6 and
Section 7.3.8 for more information.
9.5.2.10 Diagnostic LEDs (400/500/600/700/800/900 Models)
Two 7-segment hexadecimal LEDs are located on the front panel of the 500/800
/900 models. Eight individual LEDs are located on the back panel of the 400
/600/700 models. These LEDs display hexadecimal values from 00-FF. Table 47
lists the execution sequence of SROM code and the corresponding LED codes on
400/500/600/700/800/900 models. Table 46 lists the execution sequence of SROM
code and the corresponding LED codes on 300 models.
Bits <7:0> of the IOCTL ASIC system support register drive these LEDs. An
8-bit value written to these bits appears on the LEDs. See Section 7.3.11.
9–14 I/O Programming