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FUNCTIONAL OESCR! PTION
4.12 ONBOARD ROM/PROM/EPROM
The MVME135/136 module has two 28-pin JEOEC sockets that are
organized as a single bank. This bank appears as a 16-bit word port
to the MC68020 and can be configured for 32K x 8 or 64K x 8
ROM/PROM/EPROMs with an access time of 250 nanoseconds or faster,
providing a total of 128Kb of non-volatile storage.
If
32K
x
8
devices are used, they will appear twice in the 128Kb ROM/PROM/EPROM
address space.
4.13 DUAL SERIAL PORTS
For its two asynchronous serial ports, the MVME135/136 module uses
the MC68681 to provide the timing and control necessary to support
two independent communications channels.
Both serial ports utilize standard RS-232C drivers and receivers.
Signals are available through DB-9 connectors located on the
MVME135/136 module's front panel. Both ports are configured as a
9-wire
DTE
interface as illustrated in Figure 4-10.
SERIAL PORT 1
SERIAL PORT 2
1
OCO
DeO
2
RXO
RXO
J
TXO
TXO
4
OTA
OTA
5
SG
SG
6
OSR
DSR
6
7
RTS
RTS
7
8
CTS
g
FG
CTS
I :
FG
FIGURE 4-10. SERIAL PORT INTERCONNECTIONS
4.14 MVME135/136 TIMER
Timer functions for the MVME135/136 modules are provided by a Z8036
Counter/Timer and Parallel
I/O Unit.
This device offers two
independent a-bit. double-buffered, bidirectional I/O ports, three
independent 16-bit counter/timers, and a 4-bit special purpose I/O
port. The latter is used in conjunction with one counter/timer to
implement a watchdog timer and also provide a means for software
selection of a reset type.
The function of each of the timers is
described below.
4-17
I
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