CY545

Chapter 14
CY545 Output Display Support

Output Format

As mentioned in the command descriptions, the CY545 can support a number of output devices, selected by the Mode command. Two types of serial output are possible, and two types of parallel output are possible.

The CY545 generates output from the string function, for user encoded messages, and from the Query command, for current parameter values. The exact format of the output is determined by the selected display and the ASCII or Binary command mode.

For standard serial output, the power-on default, the CY545 simply transmits each character of a string or query on the serial output line, TxD. Every character between the quotes is sent for a string, and the query parameter outputs are:

Where “X” is the parameter letter (N, P, R, etc.), and “vvvvv” is the five decimal digit or eight decimal digit value of the parameter. The query output ends with a single carriage return character.

Output to LCD (CY325-Based)

When the CY325 based serial display is selected, the CY545 commands the CY325 to split the display into two sections. The right hand section is used for string outputs, and no modifications are made to the characters of a string. The left hand section of the display is used for the parameter values, with each parameter assigned a different line on the display.

When a parameter query command is received, the output of the value involves moving the display cursor to the proper display location, then printing the parameter value, and finally, moving the cursor back to the standard display area.

The CY325 is a special display control chip available from Cybernetic Micro Systems.

Output to Parallel Device
(Including CY233 Network Chip)

The standard parallel output can be used by a parallel connected host or by the CY233 Network Communications Controller. Both connections use the same signals, the parallel handshake control lines IO_REQUEST, BUSY, and FPL (USRB6).

When the CY545 receives a Query command or a string to send, it changes to the output mode internally, and lowers the FPL signal. It then waits for a low level on the IO_REQUEST signal, indicating that the host or CY233 is ready to take a character.

The character to output is placed on the data bus, and the CY545 drives the BUSY line low, indicating that a character is available.

The CY545 will now wait in this state until the host or CY233 drives IO_REQUEST high again. This indicates that the character has been accepted, so the CY545 removes the character from the data bus, and raises the BUSY line again.

This handshake process repeats until all the characters of the Query output or string have been sent. The CY545 then drives the FPL line high again, and goes back into the command mode.

A CY233 interface is included with the “CY545 Applications Example”, shown in a previous chapter.

Output to 8-Digit LED Display

The final selection for a display device is a special parallel display, using the Hewlett-Packard HDSP-211x displays. These displays are very compact, LED-based, 8 character, dot matrix displays. They have programmable intensity and custom definable character fonts.

The displays connect to the CY545 over the parallel data bus, the lower address byte, and the HP_SEL (USRB7) signal. The RD and WR strobes also provide data transfer timing for these displays.

The applications example schematic includes the proper connections for the HDSP-211x displays. This connection scheme must be used for proper operation of the displays, because the CY545 assumes the address lines are connected as shown to access the display control registers and data buffers.

When the HP display is selected, any string messages are sent to the display verbatim. Be careful that messages are not longer than 8 characters at a time. Carriage return codes are not displayed, but they reset the character address to the left most display character, and cause the display to be blanked before the next character is written.

Query command outputs follow the same format as the standard serial and parallel display outputs, except for the 8 digit values, which only display the value, so the HP displays can show one parameter value at a time. The display is blanked, and a new parameter value is written each time the Query command is used.

The CY545 takes care of any timing involved in running the HP display, and generates the proper control signals. Also, a special command ( [ ) allows you to customize the display control for your desired intensity or other functions.