20-668-0024 Rabbit Semiconductor, 20-668-0024 Datasheet - Page 259

• Manufacturer Part Number: 20-668-0024
• Description: IC CPU RABBIT4000 128-LQFP
• Manufacturer: Rabbit Semiconductor

Specifications of 20-668-0024

• Processor Type: Rabbit 4000 8-bit
• Speed: 60MHz
• Voltage: 2.5V, 2.7V, 3V, 3.3V
• Mounting Type: Surface Mount
• Package / Case: 128-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Other names: 20-668-0022; 316-1078

The strobes can be enabled to come out on Parallel Ports C, D, or E.
By default the I/O strobes are configured as read-only chip selects with 15 wait states and
normal timing. These settings will affect the /IORD, /IOWR, and /BUFEN signals for
external I/O writes even if no other strobe outputs are enabled in the parallel port registers.
24.1.3 I/O Handshake
An external I/O handshake input can be enabled on one of the Parallel Port E pins for any
combination of the I/O banks. The external device holds this signal (active high or low)
when it is busy and cannot accept a transaction. The Rabbit 4000 will then hold midway
through the transaction until either the handshake signal goes inactive or a timeout occurs.
The timeout can be defined anywhere from 32 to 2048 clocks. When the timeout occurs,
the transaction ends and a status bit is set. This bit must be checked by the program
attempting the write; no interrupt is generated.
The I/O handshake signal is sampled at the end of the first wait state (Tw). When the hand-
shake signal is disabled, the transition will start at the beginning of the Tw phase and con-
tinue to completion.
Figure 24-2. External I/O Handshake Timing Diagram
Chapter 24 External I/O Control
249