Digital Signal Processing Reference
In-Depth Information
5.8.3 Outputs
Scan_code contains the bytes transmitted by the keyboard when a key is
pressed or released. See Table 11.2 in Chapter 11 for a listing of keyboard scan
codes. Scan codes for a single key are a sequence of several bytes. A make code
is sent when a key is hit, and a break code is sent whenever a key is released.
When typing, it is normal to have several keys on a keyboard depressed at the
same time on different fingers. Also, some features require holding down
multiple keys, so several make codes may be seen before the break code for a
particular key.
Scan_ready is a handshake output signal that goes High when a new scan code
is sent by the keyboard. The read input clears scan_ready. The scan_ready
handshake line should be used to ensure that a new scan code is read only once.
