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13-Bit ANR Word Compression and Expansion Techniques

IP.com Disclosure Number: IPCOM000042452D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Gorga, KJ: AUTHOR [+2]

Abstract

Emulation of the IBM 3277 terminal with an 8-bit microprocessor involves the solution of some special problems. These result because the 3277 data interface (ANR) uses 13-bit control and data words, while the microprocessor has only 8 bits to work with. A hardware adapter card was built to perform the functions of several of the bits of the 13-bit words, such as read, write, and cursor position control. The rest of the required functions can be controlled by a software program in the microprocessor. These functions require translation of all data fields to and from the data code used by the device the data is to be sent to, i.e., keyboard, display screen, etc. The overall dataflow is shown in Fig. 1. As noted, ANR words consist of 13 bits of data.

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13-Bit ANR Word Compression and Expansion Techniques

Emulation of the IBM 3277 terminal with an 8-bit microprocessor involves the solution of some special problems. These result because the 3277 data interface (ANR) uses 13-bit control and data words, while the microprocessor has only 8 bits to work with. A hardware adapter card was built to perform the functions of several of the bits of the 13-bit words, such as read, write, and cursor position control. The rest of the required functions can be controlled by a software program in the microprocessor. These functions require translation of all data fields to and from the data code used by the device the data is to be sent to, i.e., keyboard, display screen, etc. The overall dataflow is shown in Fig. 1. As noted, ANR words consist of 13 bits of data. When using the ANR interface with an 8- bit microprocessor-based terminal, the 13-bit word must be compressed or expanded, receiving or transmitting data, to or from an 8-bit microprocessor data bus. There are four cases to consider: data to and from the Control Unit, a command word, and a status word.

See Fig. 2 for bit assignment chart. Data to the Control Unit (CU) can be expanded from 8 bits by inserting bits 1, 2, and 13 in hardware since they will never change on the same model terminal. Generate a parity bit 12 in hardware to save another bit space and use a cursor latch compared against the current DMA address to generate the cursor bit (bit 3). This leaves 8 bits of data to be loaded by the 8-bit microprocessor data bus. Da...