668-0011 Rabbit Semiconductor, 668-0011 Datasheet - Page 201

• Manufacturer Part Number: 668-0011
• Description: IC MPU RABIT3000A 55.5MHZ128LQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 668-0011

• Rohs Status: RoHS non-compliant
• Processor Type: Rabbit 3000 8-Bit
• Speed: 55.5MHz
• Voltage: 2.5V, 2.7V, 3V, 3.3V
• Mounting Type: Surface Mount
• Package / Case: 128-LQFP
• Features: -
• Other names: 316-1043

23. E
I/O C
XTERNAL
ONTROL
23.1 Overview
The Rabbit 3000’s external I/O space consists of 64 KB that is accessed by prefixing a
read or write instruction with the IOE instruction. These accesses can go onto the memory
bus or onto the external I/O bus (described below). There are three dedicated signal pins
(/IORD, /IOWR, /BUFEN) that toggle for all external I/O accesses, and eight I/O strobes
that can be associated with this external I/O space and directed out of Parallel Port E.
23.1.1 External I/O Bus
The Rabbit 3000 can enable a separate external I/O bus for external devices to keep bus
loading on the memory bus at an acceptable level. This bus consists of eight data lines on
Parallel Port A and up to six address lines on Parallel Port B. This functionality is mutu-
ally exclusive with the slave port and regular parallel I/O on Parallel Ports A and B.
When enabled, the address lines of the external I/O bus hold their value until a new value
is written to them. The data lines return to a tristate mode after each transaction.
See Section 23.1.2 for memory timing for external I/O accesses.
Chapter 23 External I/O Control
191