w65c22 Western Design Center, Inc., w65c22 Datasheet - Page 11

• Manufacturer Part Number: w65c22
• Description: W65c22n And W65c22s Versatile Interface Adapter Via Datasheet
• Manufacturer: Western Design Center, Inc.

2.3
Read Handshake Control.
Read Handshaking provides effective control of data transfers from a peripheral device to the
microprocessor. To accomplish the Read Handshake, the peripheral device generates a Data Ready signal
to the W65C22N that indicates valid data is present on PA or PB. In most cases, this Data Ready signal will
interrupt the microprocessor, which will then read the data and generate a Data Taken signal. Once the
peripheral senses the Data Taken signal, new data will be placed on the bus. This process continues until
the data transfer is complete.
Automatic Read Handshaking applies to PA only. The Data Ready signal is transmitted by the peripheral
device over the CA1 interrupt line, while the Data Taken signal is generated and transmitted to the
peripheral device over the CA2 line. When the Data Ready signal is received, it sets an internal flag in the
Interrupt Flag Register (IFR). This flag may interrupt the microprocessor or it may be polled under program
control. As an option, the Data Taken signal may be either a pulse or a level. In either case, it is set to a
Logic 0 by the microprocessor and is set by the next Data Ready signal, see Figure 2-1.
Figure 2-1 Read Handshake Operation (PA Only)
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