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Interpreting READIO and WRITIO Registers for HP 98622

(From HP BASIC Interface Reference)

Register	READIO REGISTER	MEANING	Status / Control Equivalent	WRITEIO REGISTER	MEANING	Status / Control Equivalent
0	Interface Ready	1=Ready; 0=Not Ready	Status Register 4	Set PCTL	Nonzero value: Set	Control Register 1
1	Card Identification	Always 3	Status Register 0	Reset Interface	Nonzero value: Reset	Control Register 0
2	(Undefined)	(Undefined)	NA	Interrupt Mask	See Table Below	Use ENABLE INTR Register
3	Interrupt Status	See Table below	Status Register 1	Interrupt and DMA Enable	See Table Below	Control Register 255
4	MSB of DATA IN	DI15-DI8	Status Register 3 (MSB)	MSB of DATA OUT	DO15-DO8	Control Register 3 (MSB)
5	LSB of DATA IN	DI7-DI0	Status Register 3 (LSB)	LSB of DATA OUT	DO7-DO0	Control Register 3 (LSB)
6	(Undefined)	(Undefined)	NA	(Undefined)	(Undefined)	NA
7	Peripheral Status	See Table Below	Status Register 5	Set control output lines	Bits 7-2 Not Used Bit 1 CTL1 1=LO 0=HI Bit 0 CTL0 1=LO 0=HI	Control Register 2

READIO REGISTER 3:  Interrupt Status

7	6	5	4	3	2	1	0
Interrupts are enabled	An interrupt is currently requested	Interrupt level switches (hardware priority)	Interrupt level switches (hardware priority)	Burst mode DMA	Word mode DMA	DMA Channel 1 Enabled	DMA Channel 2 Enabled
Value: 128	64	32	16	8	4	2	1

READIO REGISTER 7:  Peripheral Status

7	6	5	4	3	2	1	0
0	0	0	0	PSTS OK	EIR line low	STI1 line low	STI0 line low

WRITEIO REGISTER 2 Interrupt Mask

7	6	5	4	3	2	1	0
Not Used						Interface Ready Interrupts	EIR line Interrupts

WRITEIO REGISTER 3 Enable Interrupts and DMA

7	6	5	4	3	2	1	0
Enable Interrupts	Not Used			Enable Burst Mode DMA	Enable word mode DMA	Enable DMA Channel 1	Enable DMA Channel 0