Signetics 2661 EPCI (serial) pinout

DIP-28. The two HERO 2000 serial channels (serial A at $E8, serial B at $EC).

An enhanced programmable communications interface with its own baud-rate generator clocked on BRCLK. The HERO 2000 has two, decoded by the I/O PAL as 2661A ($E8-$EB, interrupt VI4) and 2661B ($EC-$EF, VI5); they drive the two 25-pin RS-232 connectors P410 and P412 (terminal and printer). /DCD and /CTS must be low or the receiver and transmitter stay off.

Open the interactive 2661 pinout

Pins

Pin	Name	Type	Signal
1	D2	data	Data bus bit 2.
2	D3	data	Data bus bit 3.
3	RxD	serial	Serial receive data (mark = high).
4	GND	ground	Ground.
5	D4	data	Data bus bit 4.
6	D5	data	Data bus bit 5.
7	D6	data	Data bus bit 6.
8	D7	data	Data bus bit 7 (MSB).
9	/TxC /XSYNC	clock	Transmit clock in (1x, 16x, 64x), or with the internal clock a 1x/16x clock out or external sync input.
10	A1	addr	Register select bit 1.
11	/CE	ctrl	Chip enable, active low; high floats D0-D7.
12	A0	addr	Register select bit 0.
13	R/W	ctrl	Read when low, write when high (the reverse of the 6800 sense).
14	/RxRDY	ctrl	Receiver ready, open drain; low when a character is waiting.
15	/TxRDY	ctrl	Transmitter ready, open drain; low when the holding register can take a character.
16	/DCD	serial	Data carrier detect; must be low for the receiver to run.
17	/CTS	serial	Clear to send; must be low for the transmitter to run.
18	/TxEMT /DSCHG	ctrl	Transmitter empty, or DSR/DCD change; open drain.
19	TxD	serial	Serial transmit data; held at mark when disabled.
20	BRCLK	clock	Baud-rate generator clock (4.9152 or 5.0688 MHz depending on version).
21	RESET	ctrl	Master reset, active high.
22	/DSR	serial	Data set ready, general-purpose input.
23	/RTS	serial	Request to send, general-purpose output.
24	/DTR	serial	Data terminal ready, general-purpose output.
25	/RxC /BKDET	clock	Receive clock in, or with the internal clock a 1x/16x clock out or break-detect output.
26	VCC	power	+5 V supply.
27	D0	data	Data bus bit 0 (LSB).
28	D1	data	Data bus bit 1.

Fitted in

HERO 2000 U427, U428 (I/O board, verify)

Sources

Signetics SC2661 EPCI, 1982 MOS Microprocessor Data Manual, printed p. 1-52