Casio interface chip HD61710A01

The chip HD61710A01 is the main component of the Casio interfaces MD-100, FA-7, FA-80.

interface chip HD61710A01

Pin functions

Pin	Symbol	Function
2..5	A3..A0	address signals connected to these inputs select the chip registers, the state of the input A3 seems to be ignored
6..13	IO0..IO7	bi-directional data bus
14 15 16	OE WR CS	bus interface signals
17	CNTL	input, high level = reset, low level = normal operation
18	INT	interrupt request output, active low
22,23	PON1,PON2	low level turns the power supply for the internal logic on
25	P1
26,27	OSC1,OSC2	ceramic resonator 612kHz, OSC1 is the output from the inverting oscillator amplifier
29,30	OSC3,OSC4	quartz crystal resonator 2.4576MHz, OSC4 is the output from the inverting oscillator amplifier
31	SELOSC	clock source option: high level selects the oscillator OSC1,OSC2 low level selects the oscillator OSC3,OSC4
33..40	PD7..PD0	printer data port
42 43 44	BUSY FAULT ACK	printer status port
45 46	STROBE INIT	printer control port
47..54	PA0..PA7	general purpose input port, function depends on the interface unit: FA-7 - all pins connected to VSS FA-80 - state of the print mode switches MD-100 - data read from the FDD system The calculators PB-1000 and PB-2000C read this port to determine the kind of connected device. Assignment of values: &HFF - no I/O device present &H00 - FA-7 &H55 - MD-100 (value returned directly after the reset, before any FDD transfer)
55..62	PB0..PB7	general purpose output port, function depends on the interface unit: FA-7, FA-80 - pin PB7 controls the cassette motor relay MD-100 - data written to the FDD system
65 67 68	EAR MIC PHASE	cassette interface port
70	TXD	serial port transmit data output
71 72	RTS DTR	serial port control signals
73	RXD	serial port receive data input
74 75 76	CTS DSR DCD	serial port status signals
77..79	SW0..SW2	baud rate select switches

Register addresses

A2	A1	A0	Access	Function
0	0	0	Write	serial port control register bit 0 - set when MT, cleared when RS232C bit 1 - set when parity odd, cleared when parity even bit 2 - cleared turns the parity control on bit 3 - set when 7 data bits, cleared when 8 data bits bit 4 - set when 1 stop bit, cleared when 2 stop bits bits 5..7 - baud rate
0	0	0	Read	serial port status register bit 0 - set when TX buffer full, cleared after the byte has been transmitted bit 1 - set when RX buffer full, cleared after reading the RX data register 010 bit 2 - state of the CTS input bit 3 - state of the DSR input bit 4 - state of the DCD input bit 5 - receive error flag bits 6..7 - cleared on valid carrier tone from the tape, i.e. when the frequency deviation does not exceed -30% (bit 6) to +100% (bit 7)
0	0	1	Write	serial port control register bit 0 - transmitter enable bit 1 - receiver enable bit 2 - state of the RTS output bit 3 - state of the DTR output
0	0	1	Read	serial port status register bits 0..2 - receive errors bit 3 - state of the SW0 input bit 4 - state of the SW1 input bit 5 - state of the SW2 input
0	1	0	Write	serial port control register bit 0 - interrupt request when RX buffer full
0	1	0	Read	serial port receive data register
0	1	1	Write	serial port transmit data register
0	1	1	Read	general purpose input port PA
1	0	0	Write	general purpose output port PB
1	0	0	Read	printer status port bit 0 - state of the BUSY input bit 1 - state of the FAULT input bit 2 - set by a pulse on the ACK input, reset by writing logical 1 to the bit 2 of register 110 bits 3..7 are expected to be 0
1	0	1	Write	printer data port PD
1	1	0	Write	printer control port bit 0 - state of the STROBE output bit 1 - state of the INIT output bit 2 - logical 1 resets the ACK latch

Baud rate selects

bits 765	baud rate
000	9600
001	4800
010	2400
011	1200
100	600
101	300
110	150
111	75

Receive errors

Information about those bits, extracted from various ROM disassembly listings, is inconsistent.

PB-1000 and PB-2000C, discarded interrupt service routine in the internal ROM

If the error flag in the register 000 is set, then the contents of the register 001 is examined to determine the exact cause:

if bit 0 is set, then a framing error has occurred
else if bit 1 is set, then a parity error has occurred
otherwise an overrun error has occurred

PB-1000 and PB-2000C, replacement interrupt service routine in the external ROM (probably most trustworthy)

If the error flag in the register 000 is set, then the contents of the register 001 is examined:

if bit 0 is set, then a parity or overrun error has occurred
else if bit 1 is cleared, then a framing error has occurred
otherwise the transfer is assumed to be error-free

FX-8000G, interrupt service routine in the external ROM

The error flag in the register 000 isn't checked, but a general "read error" is reported when any of the bits 0..2 in the register 001 is set.

Test results

the error flag in the register 000 is set by any receive error
bit 0 in the register 001 is set by a parity error
bit 1 in the register 001 is set by an overrun error
bit 2 in the register 001 is set by a framing error
all these flag bits are updated on every received data byte