SERIAL ATN OUT: (SERIAL ATTENTION OUT)

The Commodore 64 uses this signal to start a command sequence for a device on the serial bus. When the Commodore 64 brings this signal LOW, all other devices on the bus start listening for the Commodore 64 to transmit an address. The device addressed must respond in a preset period of time; otherwise, the Commodore 64 will assume that the device addressed is not on the bus, and will return an error in the STATUS WORD. (See Figure 6-4).

SERIAL BUS TIMING

Description	Symbol	Min.	Typ.	Max.
ATN RESPONSE (REQUIRED)1	TAT	-	-	1000µs
LISTENER HOLD-OFF	TH	0	-	infinite
NON-EOI RESPONSE TO RFD2	TNE	-	40µs	200µs
BIT SET-UP TALKER4	TS	20µs	70µs	-
DATA VALID	TV	20µs	20µs	-
FRAME HANDSHAKE3	TF	0	20	1000µs
FRAME TO RELEASE OF ATN	TR	20µs	-	-
BETWEEN BYTES TIME	TBB	100µs	-	-
EOI RESPONSE TIME	TYE	200µs	250µs	-
EOI RESPONSE HOLD TIME5	TEI	60µs	-	-
TALKER RESPONSE LIMIT	TRY	0	30µs	60µs
BYTE-ACKNOWLEDGE4	TPR	20µs	30µs	-
TALK-ATTENTION RELEASE	TTK	20µs	30µs	100µs
TALK-ATTENTION ACKNOWLEDGE	TDC	0	-	-
TALK-ATTENTION ACK. HOLD	TDA	80µs	-	-
EOI ACKNOWLEDGE	TFR	60µs	-	-

Notes:
1.	If maximum time exceeded, device not present error.
2.	If maximum time exceeded, EOI response required.
3.	If maximum time exceeded, frame error.
4.	Tv and Tpr minimum must be 60µs for external device to be a talker.
5.	Tei minimum must be 80µs for external device to be a listener.