Rabbit 2000 - Page 59

User’s Manual 53
Status
SMODE1
SMODE0
Input
Startup mode select (SMODE1 = pin 35,
SMODE0 = pin 36) to determine bootstrap
procedure.
(SMODE1 = 0, SMODE0 = 0) start
executing at address zero.
(0,1) cold boot from slave port.
(1,0) cold boot from clocked serial port A.
(1,1) cold boot from asynchronous serial
port A at 2400 bps.
The SMODE pins can be used as general
input pins once the cold boot is complete.
35–36 (1:0)
Chip
Selects
/CS0 Output
Memory Chip Select 0—connects directly
to static memory chip select pin. Normally
this pin is used to select base flash memory
that holds the program.
8
/CS1 Output
Memory Chip Select 1—normally this pin
is connected directly to static RAM chip
select. /CS1 can be optionally forced
continuously low under software control, a
feature that aids in the use of battery-
backed RAM when the chip select must
pass through a controller that may have a
slow propagation time.
5
/CS2 Output
Memory Chip Select 2—connect to static
memory chip. Use this chip select last.
4
Output
Enables
/OE0 Output
Memory Output Enable 0—connect
directly to static memory chip.
6
/OE1 Output
Memory Output Enable 1—alternate
memory output enable allows chip selects
to be shared between two memory chips.
76
Write
Enables
/WE0 Output
Memory Write Enable 0—connect directly
to static memory chip. This pin may be
disabled under software control to write
protect the chip.
69
/WE1 Output
Memory Write Enable 1—connect directly
to static memory chip. This pin may be
disabled under software control to write
protect the chip.
80
I/O Control /BUFEN Output
I/O Buffer Enable—this signal is driven
low during an external I/O cycle and may
be used to control 3-state enable on the bus
buffer. The purpose is to save power by not
driving the I/O address or data lines on
every bus cycle.
33
Table 5-1. Rabbit Pin Descriptions (continued)
Pin Group Pin Name Direction Function Pin Numbers