BCR Port Access - Revision history

Jhoger at 07:00, 31 January 2009

2009-01-31T07:00:13Z

← Older revision		Revision as of 00:00, 31 January 2009
Line 43:		Line 43:
	In order to account for the inconsistency, always use pin 7 of the BCR		In order to account for the inconsistency, always use pin 7 of the BCR
	connector for circuit COMMON, and never rely on the use of pin 5.		connector for circuit COMMON, and never rely on the use of pin 5.

			[[Category:Model T Developer Reference]]

Jhoger at 07:46, 5 December 2008

2008-12-05T07:46:21Z

← Older revision		Revision as of 00:46, 5 December 2008
Line 33:		Line 33:
	whether the Wand is passing over a thin Bar code line or a think Bar code		whether the Wand is passing over a thin Bar code line or a think Bar code
	line.		line.

			Note that there is inconsistency among Model 10x laptops in regard to the appearance of
			circuit COMMON at the Bar Code Reader (BCR) connector. Various Tandy
			publications indicate that circuit COMMON, which Tandy designates as GND,
			appears both at pin 5 and at pin 7 of the BCR connector. However, this is not
			the case for all Model 10x laptops. Pin 5 of some Model 10x laptops does not
			present circuit COMMON -- that's the inconsistency.

			In order to account for the inconsistency, always use pin 7 of the BCR
			connector for circuit COMMON, and never rely on the use of pin 5.

Jhoger at 07:38, 5 December 2008

2008-12-05T07:38:06Z

← Older revision		Revision as of 00:38, 5 December 2008
Line 4:		Line 4:
	capabilities. It also can supply +5V to a device connected to the port.		capabilities. It also can supply +5V to a device connected to the port.

	The ~~BCR~~ input signal is connected to two places		The input signal is connected to two places
	within the laptop: at I/O Port 179 where it appears at bit position 3, and at		within the laptop: at I/O Port 179 where it appears at bit position 3, and at
	the 8085C CPU where it appears at the RST5.5 interrupt request signal input		the 8085C CPU where it appears at the RST5.5 interrupt request signal input
	pin.		pin.

	The ~~BCR~~ input appearance at the RST5.5		The input appearance at the RST5.5
	interrupt request signal input pin of the 8085C CPU can generate an		interrupt request signal input pin of the 8085C CPU can generate an
	interrupt, and its state can be read using the RIM instruction.		interrupt, and its state can be read using the RIM instruction.

Jhoger at 07:37, 5 December 2008

2008-12-05T07:37:17Z

← Older revision		Revision as of 00:37, 5 December 2008
Line 3:		Line 3:
	The BCR interface has only a single bit of input and no output		The BCR interface has only a single bit of input and no output
	capabilities. It also can supply +5V to a device connected to the port.		capabilities. It also can supply +5V to a device connected to the port.

	The BCR input signal is connected to two places		The BCR input signal is connected to two places
	within the laptop: at I/O Port 179 where it appears at bit position 3, and at		within the laptop: at I/O Port 179 where it appears at bit position 3, and at

Jhoger at 07:36, 5 December 2008

2008-12-05T07:36:45Z

← Older revision		Revision as of 00:36, 5 December 2008
Line 1:		Line 1:
	From Ron Wiesen:		From Ron Wiesen:

	The BCR interface ~~in input~~ has only a single bit of input and no output		The BCR interface has only a single bit of input and no output
	capabilities.		capabilities. It also can supply +5V to a device connected to the port.

	The BCR input signal is connected to two places		The BCR input signal is connected to two places
	within the laptop: at I/O Port 179 where it appears at bit position 3, and at		within the laptop: at I/O Port 179 where it appears at bit position 3, and at

Jhoger: New page: From Ron Wiesen: The BCR interface in input has only a single bit of input and no output capabilities. The BCR input signal is connected to two places within the laptop: at I/O Port 179 ...

2008-12-05T07:35:13Z

New page: From Ron Wiesen: The BCR interface in input has only a single bit of input and no output capabilities. The BCR input signal is connected to two places within the laptop: at I/O Port 179 ...

New page

From Ron Wiesen:

The BCR interface in input has only a single bit of input and no output
capabilities.

The BCR input signal is connected to two places
within the laptop: at I/O Port 179 where it appears at bit position 3, and at
the 8085C CPU where it appears at the RST5.5 interrupt request signal input
pin.

The BCR input appearance at the RST5.5
interrupt request signal input pin of the 8085C CPU can generate an
interrupt, and its state can be read using the RIM instruction.

Executing RIM
will copy the interrupt mask to the "A" register. The mask allows/prevents generation of an
interrupt due to the BCR input.

However, executing the RIM instruction also copies the state of the RST5.5
interrupt request signal (as well as the RST6.5 and RST7.5 interrupt request
signals) to the "A" register, and this also is relevant to the BCR input.

Executing the RIM instruction copies the state
of the RST5.5 interrupt request signal (i.e., the state of BCR input) to the
"A" register where it will be deposited at bit position 4.

As I understand it, the BCR drivers (i.e., the Tandy provided discriminator
software) unmask the the RST5.5 interrupt request signal and, upon a
subsequent generation of the RST5.5 interrupt, are invoked by the interrupt.
Upon an invocation, the BCR drivers repeatedly use the IN instruction to
inspect the BCR input appearance at bit position 3 of I/O Port 179 while
measuring the duration of its two sustained states in order to ascertain
whether the Wand is passing over a thin Bar code line or a think Bar code
line.