DE LA INVESTIGACIÓN EMPÍRICA
8.1. ANÁLISIS DE LA VALIDEZ
8.2.2. Agenda viso-espacial
2 0 0 0 0 1 1 1 1 0 0 0 1 0 0 1 1 0 0 1 1 0 0 1 0 0 1 0 1 0 1 0 1 0 1 0 Bit Value 0/$0 1/*1 2/$2 3/$3 4/$4 5/$5 6/$6 7/%7 8/$8 9/$9 10/$A Baud rate user defined 50 75 110 134. 150 300 600 1200 1800 2400 baud baud baud 5 baud baud baud baud baud baud baud
When the user-defined rate is selected, the baud rate is deter- mined by the value in locations 2578-2579/$0A12-$0A13. The remaining possible bit patterns, %1011-%llll/ result in
invalid baud rates. Bit 4: Unused.
Bits 5-6: These bits determine the number of data bits in each character sent or received (sometimes referred to as the word size). The total character length will also include a start bit, possibly a parity bit, and one or more stop bits.
Bits Bit Number of 6 5 value data bits 0 0 0/$00 8 data bits 0 1 32/$20 7 data bits 1 0 64/$40 6 data bits 1 1 96/S60 5 data bits
Bit 7: This bit determines the number of stop bits in each character. Stop bits are %1 bits added to the end of the char- acter. They represent the minimum amount of time the com- munications line will remain at the low (%1 bit) level before the next start bit can be sent or received.
Bit 7 Bit value 0 0/$00 1 128/S80
Number of stop bits 1 stop bit
2 stop bits
M51CDR
2577 $OA11
RS-232 command register
This location controls some of the operating characteristics of the RS-232 interface. When a file is opened to device 2, the
126
$ O A 1 1 2 5 7 7
second character of the filename, if any, is copied here. Al- though RS-232 communications in the 128 are managed by software, the bits of this location are defined to simulate the command register of a 6551 UART chip, a hardware device for controlling serial communications. The bits are used as follows: Bit 0: This bit controls the handshaking mode for RS-232 transmission and reception. The RS-232 interface consists of three primary signal lines—transmitted data, received data, and ground—plus a number of supplementary control lines— data set ready (DSR), data terminal ready (DTR), ready to send (RTS), and clear to send (CTS). The control lines are called handshaking lines because they allow the sending and receiv- ing units to exchange signals (handshakes) indicating whether data is being successfully transmitted and received. The 128's RS-232 software interface can operate in two different modes: 3-line, where none of the handshaking lines are used, and x- line, where all of the handshaking lines are used. These bits control the interface mode as follows:
Bit 0 Interface mode
0 3-line interface {no handshaking) 1 x-line interface {full handshaking)
For 3-line mode, the output handshaking lines (DTR and RTS) will be held at a constant high ( + 5 volts) level. The input handshaking lines {DSR and CTS) will be ignored.
Bits 1-3: Unused.
Bit 4: For unknown reasons, Commodore literature continues
to indicate that this bit controls the duplex mode of the RS- 232 interface. The bit is supposed to select full duplex when set to %0 or half duplex when set to % 1 . However, this bit is not checked by any RS-232 routine, and its setting has no ef- fect on the operation of the interface.
Duplex is often confused with local echo. A full-duplex interface can simultaneously send and receive data, while a half-duplex interface can send data and receive data, but not both at the same time. The 128's RS-232 interface always op- erates in full-duplex mode. In casual usage, however, duplex is often used to describe whether or not the system echoes back the characters it receives. In remote echo mode {incorrectly re- ferred to as full duplex), the system displays only characters received from the remote unit (the one being called). The as- sumption is that the remote unit will send back an "echo" of
2577 $OA11 3 0 0 0 0 0 0 0 0 1 1 1 Bits 2 0 0 0 0 1 1 1 1 0 0 0 1 0 0 1 1 0 0 1 1 0 0 1 0 0 1 0 1 0 1 0 1 0 1 0 Bit Value 0/$0 1/*1 2/$2 3/$3 4/$4 5/$5 6/$6 7/%7 8/$8 9/$9 10/$A Baud rate user defined 50 75 110 134. 150 300 600 1200 1800 2400 baud baud baud 5 baud baud baud baud baud baud baud
When the user-defined rate is selected, the baud rate is deter- mined by the value in locations 2578-2579/$0A12-$0A13. The remaining possible bit patterns, %1011-%llll/ result in
invalid baud rates. Bit 4: Unused.
Bits 5-6: These bits determine the number of data bits in each character sent or received (sometimes referred to as the word size). The total character length will also include a start bit, possibly a parity bit, and one or more stop bits.
Bits Bit Number of 6 5 value data bits 0 0 0/$00 8 data bits 0 1 32/$20 7 data bits 1 0 64/$40 6 data bits 1 1 96/S60 5 data bits
Bit 7: This bit determines the number of stop bits in each character. Stop bits are %1 bits added to the end of the char- acter. They represent the minimum amount of time the com- munications line will remain at the low (%1 bit) level before the next start bit can be sent or received.
Bit 7 Bit value 0 0/$00 1 128/S80
Number of stop bits 1 stop bit
2 stop bits
M51CDR
2577 $OA11
RS-232 command register
This location controls some of the operating characteristics of the RS-232 interface. When a file is opened to device 2, the
126
$ O A 1 1 2 5 7 7
second character of the filename, if any, is copied here. Al- though RS-232 communications in the 128 are managed by software, the bits of this location are defined to simulate the command register of a 6551 UART chip, a hardware device for controlling serial communications. The bits are used as follows: Bit 0: This bit controls the handshaking mode for RS-232 transmission and reception. The RS-232 interface consists of three primary signal lines—transmitted data, received data, and ground—plus a number of supplementary control lines— data set ready (DSR), data terminal ready (DTR), ready to send (RTS), and clear to send (CTS). The control lines are called handshaking lines because they allow the sending and receiv- ing units to exchange signals (handshakes) indicating whether data is being successfully transmitted and received. The 128's RS-232 software interface can operate in two different modes: 3-line, where none of the handshaking lines are used, and x- line, where all of the handshaking lines are used. These bits control the interface mode as follows:
Bit 0 Interface mode
0 3-line interface {no handshaking) 1 x-line interface {full handshaking)
For 3-line mode, the output handshaking lines (DTR and RTS) will be held at a constant high ( + 5 volts) level. The input handshaking lines {DSR and CTS) will be ignored.
Bits 1-3: Unused.
Bit 4: For unknown reasons, Commodore literature continues
to indicate that this bit controls the duplex mode of the RS- 232 interface. The bit is supposed to select full duplex when set to %0 or half duplex when set to % 1 . However, this bit is not checked by any RS-232 routine, and its setting has no ef- fect on the operation of the interface.
Duplex is often confused with local echo. A full-duplex interface can simultaneously send and receive data, while a half-duplex interface can send data and receive data, but not both at the same time. The 128's RS-232 interface always op- erates in full-duplex mode. In casual usage, however, duplex is often used to describe whether or not the system echoes back the characters it receives. In remote echo mode {incorrectly re- ferred to as full duplex), the system displays only characters received from the remote unit (the one being called). The as- sumption is that the remote unit will send back an "echo" of
2577
$OA11
each character it receives from the system. In local echo mode (incorrectly called half duplex), the system displays the charac- ters it sends as well as the ones it receives. The assumption in this case is that the remote unit will not echo the characters it receives.
Bits 5-7: This bit controls the parity generated for transmitted characters and the parity tested for in received characters. Par- ity is a simple method of detecting some errors in data trans- mission. A parity bit can be added between the data and stop bits in the character. The value of the parity bit is selected to make the total number of %1 bits in the character (not count- ing stop bits) either even or odd. The receiving unit can then count the number of %1 bits in the received character to de- termine if bits have been garbled in transmission. Parity checking did not work properly in the original versions of the Commodore 64 Kernal ROM, but that problem has been cor- rected in the 128's Kernal (and in the version of 64 Kernal ROM for the 128's 64 mode). Possible parity selections are as follows:
Bits Parity selection 7 6 5
x x 0 parity not used 0 0 1 odd parity O i l even parity 10 1 mark parity 1 1 1 space parity
If bit 5 is %0, no parity bit will be generated in transmit- ted characters and the system will expect incoming characters to have no parity bit. This selection is common when a word size of eight data bits per character is used. Odd parity means that a parity bit will be generated for each transmitted charac- ter such that the character will have an odd total number of %1 bits (not counting the stop bits). When even parity is se- lected, the parity bit will be set to make the total number of
%1 bits in the character even. For either even or odd parity, the number of %1 bits in each character received will be counted and compared against the parity selection. If the num- ber does not match the specified parity type, the error will be indicated by setting bit 0 of the status register location (2580/ $0A14) to % 1 . Mark and space parity are alternate forms of no parity. When mark parity is selected, the parity bit for each transmitted character will always be set to % 1 , and the parity 128
S 0 A 1 4
2580
bit for each received character will be ignored. When space parity is selected, the transmitted parity bit will always be %0 and the received parity bit will be ignored.