DIGITAL-LOGIC MICROSPACE MSM800SEV, Technical User'S Manual

Page: 19 / 92

DIGITAL-LOGIC AG
MSM800 SEV Manual V1.0A
19
IRQ[ 10 12, 14, 15], input
These signals are used to tell the microprocessor that an I/O device needs attention. An interrupt request is
generated when an IRQ line is
raised from low to high . The line must be held high until the microprocessor
acknowledges the interrupt request.
/Master, input
This signal is used with a DRQ line to gain control of the system. A processor or DMA controller on the I/0
channel may issue a DRQ to a DMA channel in cascade mode and receive a /DACK.
/MEMCS16, input
MEMCS16 Chip Select signals the system board if the present data transfer is a 1 wait-state, 16-Bit, memory
cycle. It must be derived from the decode of LA17 through LA23. /MEMCS16 should be driven with an open
collector (300 ohm pull-up) or tri-state driver capable of sinking 2OmA.
/MEMR input/output
These signals instruct the memory devices to drive data onto the data bus. /MEMR is active on all memory
read cycles. /MEMR may be driven by any microprocessor or DMA controller in the system. When a micro-
processor on the I/0 channel wishes to drive /MEMR, it must have the address lines valid on the bus for one
system clock period before driving /MEMR active. These signals are
active low .
/MEMW, input/output
These signals instruct the memory devices to store the data present on the data bus. /MEMW is active in all
memory read cycles. /MEMW may be driven by any microprocessor or DMA controller in the system. When a
microprocessor on the I/O channel wishes to drive /MEMW, it must have the address lines valid on the bus
for one system clock period before driving /MEMW active. Both signals are
active low.
OSC, output
Oscillator (OSC) is a high-speed clock with a 70 nanosecond period (14.31818 MHz). This signal is not syn-
chronous with the system clock. It has a 50% duty cycle. OSC starts 100
µ
s after reset is inactive.
RESETDRV, output
Reset Drive is used to reset or initiate system logic at power-up time or during a low line-voltage outage. This
signal is active high. When the signal is active all adapters should turn off or tri-state all drivers connected to
the I/O channel. This signal is driven by the permanent Master.
/REFRESH, input/output
These signals are used to indicate a refresh cycle and can be driven by a microprocessor on the I/0 channel.
These signals are
active low .
SAO-SA19, LA17 - LA23 input/output
Address bits 0 through 19 are used to address memory and I/0 devices within the system. These 20 address
lines, allow access of up to 1MBytes of memory. SAO through SA19 are gated on the system bus when
BALE is high and are latched on the falling edge of BALE. LA17 to LA23 are not latched and addresses the
full 16 MBytes range. These signals are generated by the microprocessors or DMA controllers. They may
also be driven by other microprocessor or DMA controllers that reside on the I/0 channel. The SA17-SA23
are always LA17-LA23 address timings for use with the MSCS16 signal. This is advanced AT96 design. The
timing is selectable with jumpers LAxx or SAxx.
/SBHE, input/output
Bus High Enable (system) indicates a transfer of data on the upper byte of the data bus, XD8 through XD15.
Sixteen-Bit devices use /SBHE to condition data-bus buffers tied to XD8 through XD15.